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OPHTHALMIC 
NEURO- MYOLOGY 


A  STUDY  OF  THE  NORMAL  AND  ABNORMAL  ACTIONS  OF  THE 

OCULAR  MUSCLES  FROM  THE  BRAIN  SIDE 

OF  THE  QUESTION 


G.  C.  SAVAGE,  M.   D. 


Professor  of  Ophthalmology   in   the   Medical   Department  of   Vanderbilt  University;    Author   of       Nev 

Truths  in  Ophthalmology  "  (1895) ,  of   "Ophthalmic    Myology  "( 1901) ;    Ex-President 

of  the  Nashville  Academy  of  Medicine;   Ex-President  of  the 

Tennessee  State  Medical  Association 


Thirty-nine  Full  Page  Plates  and  Twelve  Illustrative  Figures 


PUBLISHED  BY 

The  Author,  157  Eighth  Avenue,  North,  Nashville,  Tenn. 

PRINTED   BY 

Keelin-W'illiams  Printing  Co.,  Nashville,  Tenn. 


r-  oa>< 


Entered,  according  to  the  Act  of  Congress,  in  the  year  1905, 

By  G.  C.  Savage, 

In  the  Office  of  the  Librarian  of  Congress. 
All  rights  reserved. 


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PREFACE.  — ~^ 

It  has  long  been  the  desire  of  the  author  to  help  make  the 
ocular  muscle  problem  easy  of  solution.  With  this  object  in 
view  he  undertook  the  study  of  the  normal  and  abnormal  actions 
of  the  ocular  muscles,  from  the  brain  side  of  the  question.  The 
results  of  this  labor  are  set  forth  in  this  book,  which  might  be 
entitled  "The  Muscle  Study  Made  Easy;"  but  the  title  chosen 
is  Opthalmic  Neuro-Myology,  the  name  implying  the  nature 
of  the  study. 

This  book  is  intended  as  a  companion  volume  to  Ohthalmic 
Myology.  In  the  light  of  this  newer  study,  not  a  word  need 
be  changed,  in  the  older  treatise,  concerning  the  detection  and 
treatment  of  heterophoric  conditions. 

The  hypothesis  on  which  Opthalmic  Neuro-Myology  is 
founded,  may  be  stated  as  follows:  There  are  eight  conjugate 
brain  centers,  in  the  cortex,  by  means  of  which  the  several 
versions  are  effected,  and  one  conjugate  center  by  which  con- 
vergence is  caused.  These  conjugate  centers  act  alike  on  ortho- 
phoric  and  heterophoric  eyes,  and  when  there  is  only  one  eye. 
Each  of  these  is  connected  with  two  muscles,  and  the  work 
done  by  the  center  and  its  muscles,  under  the  guidance  of  volition, 
is  normal  work.  The  conjugate  centers  have  no  causal  relation- 
ship with  the  heterophoric  conditions,  nor  have  they  any  power 
for  correcting  them. 

There  are  twelve  basal  centers,  each  connected  with  only 
one    muscle.       If    the    eyes    are    emmetropic-orthophoric,    these 

(ill) 


M282512 


,v  PREFACE. 

centers  are  forever  at  rest;  but  when  there  is  any  form  of  hetero- 
phoria,  one  or  more  of  these  centers  must  be  ever  active,  during 
all  working'  hours.  These  centers  do  not  cause  heterophoria, 
but  they  stand  ready  to  correct  it.  Under  the  guidance  of  the 
fusion  faculty,  each  basal  center  stands  ready  to  act  on  its  muscle, 
whenever  there  is  a  condition  that  would  cause  diplopia.  They 
mav  be  called  fusion  centers. 

If  the  above  hypothesis  accounts  for  every  phenomenon  con- 
nected with  the  normal  and  abnormal  actions  of  the  ocular 
muscles,  as  it  seems  to  do,  then  it  ceases  to  be  an  hypothesis 
and  becomes  a  scientific  fact. 

Plates  I  to  XXXVII  were  executed,  after  the  design  of  the 
author,  by  his  niece,  Miss  Christine  Johnson,  for  which  she 
deserves  this  public  acknowledgment. 

For  the  mechanical  excellencies  of  the  volume,  the  author, 
who  is  also  the  publisher,  is  indebted  to  the  printing  establish- 
ment whose  inscription  can  be   found    on    the    title-page. 


ILLUSTRATIONS. 


The  Ocular  Nerves. 

PLATES    I.  TO  VI. 

Plate  I.  —  Represents  the  connection  between  basal  and  cortical  centers  and 

ocular  muscles,  by  way  of  right  third  nerve  cable  64 

Plate  II. — The  brain  and  muscle  connections  through  left  third  nerve  cable  65 
Plate  III. — The  brain  and  muscle  connections  through   the    right    fourth 

nerve  cable 70 

Plate  IV. — The  brain  and  muscle  connections  through  the  left  fourth  nerve 

cable 71 

Plate  V. — The  brain  and  muscle  connections  through  the  right  sixth  nerve 

cable 74 

Plate  VI. — The  brain  and  muscle  connections  through  the  left  sixth  nerve 

cable 75 

Emmetropic-Orthophoric  Eyes. 

PLATES  VII.    TO  XVI. 

Plate  VII.  —  Brain  and  muscle  rest,  in  direct  distant  vision  78 

Plate  VIII. — Brain  center  and  muscle  activity  in  accommodation-convergence  79 

Plate  IX.  —  Brain  center  and  muscle  activity  in  right  version 84 

Plate  X. — Brain  center  and  muscle  activity  in  left  version 85 

Plate  XI.  —  Brain  center  and  muscle  activity  in  superversion 88 

Plate  XII, — Brain  center  and  muscle  activity  in  subversion 89 

Plate  XIII. — Brain  center  and  muscle  activity  in  right-up  oblique  version.  90 

Plate  XIV  — Brain  center  and  muscle  activity  in  left-down  oblique  version  91 

Plate  XV. — Brain  center  and  muscle  activity  in  left-up  oblique  version  94 

Plath  XVI. — Brain  center  and  muscle  activity  in  right-down  oblique  version  95 

Emmbtrophic-Esophoric  Eyes. 

PLATES  XVII,  TO  XX. 

Plate  XVII. — Brain  center  and  muicle  activity  in  straight-forward  distant 

vision  98 

(v) 


vi  ILLUSTRATIONS. 

Plate  XVIII. — Brain  center  and  muscle  activity  in  accommodation-con- 
vergence    99 

Plate  XIX. — Brain  center  and  muscle  activity  in  right  version  ioo 

Plate  XX.  —  Brain  center  and  muscle  activity  in  left  version 101 

Emmetropic-Exophoric  Eyes. 

PLATES  XXI.  TO  XXIV. 

Plate  XXI. — Brain   center  and   muscle   activity  in  straight-forward  distant 

vision  1 06 

Plate  XXII.  —  Brain  center  and  muscle  activity  in  accommodation-converg- 
ence    107 

Plate  XXIII. — Brain  center  and  muscle  activity  in  right  version  108 

Plate  XXIV. — Brain  center  and  muscle  activity  in  left  version 109 

Emmetropic  Hyper-  and  Cataphoric  Eyes. 

PLATES  XXV.  TO  XXVII. 

Plate  XXV. — Brain  center  and  muscle  activity  in  straight-forward  vision ....   112 

Plate  XXVI. — Brain  center  and  muscle  activity  in  superversion 114 

Plate  XXVII.  —  Brain  center  and  muscle  activity  in  subversion 115 

Emmetropic  and  Cyclophoric  Eyes. 

plates  XXVIII.  TO  XXXI. 
Plate  XXVIII. — Brain   center    (possible)    and   muscle  activity    in    distant 

vision  of  plus  cyclophoric  eyes  118 

More  probable  brain  center  activity  is  shown  in  Plate  XXXVI 178 

Plate  XXIX. — Brain  center  an  muscle  activity  in  subversion  of  plus  cyclo- 
phoric eyes 119 

Plate  XXX. — Brain  center  (possible)  and  muscle  activity  in  distant  vision 

of  minus  cyclophoric  eyes 122 

More  probable  brain  center  activity  is  shown  in  Plate  XXXVII 179 

Plate  XXXI. — Brain  eenter   and    muscle    activity   in    subversion  of    minus 

cyclophoric  eyes 123 

Ametropic  and  Heterophoric  Eyes. 

Plate  XXXII. — Brain  center  and  muscle  activity  in  convergence  of  myopic- 

orthophoric  eyes 138 


ILLUSTRATIONS.  vii 

Plate  XXXIII. — Brain  center  (possible)  and  muscle  activity  in  direct  dis- 
tant vision  of  myopic-exophoric  eyes 139 

More  probable  brain  center  activity  is  shown  in  Plate  XXI  106 

Plate  XXXIV.— Brain  center  and  muscle  activity  in  direct  distant  vision  of 

hyperopic-orthophoric  eyes 146 

Plate  XXXV. — Brain  center  and  muscle  activity  in  both  far  and  near  see- 
ing of  hyperopic-exophoric  eyes 158 

Plate  XXXVI. — Brain  center  and  muscle  activity  in  direct  distant  vision  of 
oblique  astigmatic  eyes,  with  meridians  of  greatest  curvature 
in  upper  temporal  quadrants 178 

Plate  XXXVII. — Brain  center  and  muscle  activity  in  direct  distant  vision 
of  oblique  astigmatic  eyes,  with  meridians  of  greatest  curv- 
ature in  upper  nasal  quadrants. 179 

Plate  XXXVIII. — Shows  absence  of  torsion  in  the  fusion  of  the  images  of  a 

rectangle,  in  vertical  and  horizontal  astigmatism 182 

Plate  XXXIX. — Shows  torsioning  necessary  for  fusing  the  two  images  of  a 

rectangle,  in  non-symmetric  oblique  astigmatism 183 

Illustrative  Cuts. 

Fig.     i. — Illustrates  plus  cyclophoria  of  left  eye 24 

Fig.    2. — Illustrates  minus  cyclophoria  of  left  eye 24 

Fig.     3. — Illustrates  plus  cyclophoria  of  right  eye 25 

Fig.    4. — Illustrates  minus  cyclophoria  of  right  eye 25 

Fig.     5. — Illustrates  retinal  fusion  area 39 

Fig.     6. — Illustrates  visual  results  of  unequal  refraction 164 

Fig.     7. — Shows  character  of  images  of    a  horizontal  arrow  in    vertical  or 

horizontal  astigmatic  eyes 172 

Fig.     8.— Shows  oblique  images  of  a  horizontal  arrow  in  symmetric  oblique 

astigmatic  eyes '173 

Fig.     9. — Shows  oblique  image  in  right  eye  and  horizontal  image  in  left  eye   174 
Fig.  10. — Shows  oblique  image  in  right  eye  and  horizontal  image  in  left  eye  175 
Fig.  11. — Shows  character  of  images  in  oblique  astigmatic  eyes,  when  me- 
ridians of  greatest  curvature  diverge  176 

Fig.  12. — Shows  character  of  images  in  oblique  astigmatic  eyes,  when  merid- 
ians of  greatest  curvature  converge 177 


Ophthalmic  Neuro-Myology. 


CHAPTER  I. 


OCULAR  ROTATIONS  AND  THE  MUSCLES 
EFFECTING  THEM. 


The  nervo-muscular  mechanism,  by  which  the  eyes  are 
moved,  cannot  be  properly  understood  in  the  absence  of  a 
correct  understanding  of  the  globes  that  are  to  be  rotated. 

It  is  as  strange  as  it  is  true  that  the  poles  of  the  eye  have 
not  been  correctly  located  by  previous  investigators.  Error 
in  locating  the  poles  led  to  the  greater  error  of  falsely  locat- 
ing the  axes  of  all  rotations.  These  errors  have  been 
pointed  out  in  Ophthalmic  Myology,  but  not  so  clearly  nor 
so  forcibly  as  the  author  hopes  to  do  in  this  little  book. 
A  wrong  beginning  means  a  wrong  ending.  The  error  in 
locating  the  poles  was  in  first  selecting  the  center  of  the 
cornea  for  the  anterior  pole,  and  then  locating  the  posterior 
pole  by  extending  a  line  from  the  supposed  anterior  pole, 
through  the  center  of  rotation,  to  the  retina.  This  line 
was  called,  or  miscalled,  the  optic  axis,  or  the  anteropos- 
terior axis.     By  it  the  posterior  pole  was  located,  as  a  rule, 


2  OCULAR   ROTATIONS   AND   THE 

between  the  macula  and  the  optic  disc,  rarely  at  the  macula, 
and  more  rarely  still  to  the  temporal  side  of  the  macula. 

At  the  Saratoga  meeting  of  the  American  Medical  Asso- 
ciation, in  1902,  twelve  of  the  leading  Ophthalmologists 
present  were  asked  this  question:  "At  what  point  in  the 
retina  do  all  the  corneo-retinal  meridians  cross?"  With  but 
little  hesitation  on  the  part  of  any  one,  they  all  answered, 
"at  the  center  of  the  macula."  In  thus  answering  they 
all  placed  the  posterior  pole  at  the  fovea  centralis;  for  a 
pole  is  that  point  in  a  spherical  surface  through  which  all 
the  meridians  pass.  Since  the  posterior  pole  is  always  de- 
termined by  the  location  of  the  macula,  it  becomes  evident 
that,  in  constructing  the  optic  axis,  the  beginning  should 
be  made  at  the  fovea  centralis,  that  it  should  then  be  car- 
ried through  the  center  of  rotation,  and  thence  to  that  point 
of  the  cornea  through  which  it  would  pass,  if  prolonged, 
regardless  of  whether  it  be  the  center  of  the  cornea,  or  on 
either  the  nasal  or  temporal  side  of  the  center.  This  point 
on  the  cornea  is  180°  from  the  center  of  the  macula,  or 
posterior  pole,  and  it  must  be  the  anterior  pole,  for  the  two 
poles  of  a  sphere  are  180°  degrees  apart.  The  straight  line 
connecting  these  poles  is  not  only  the  true  antero-posterior 
axis  of  the  globe,  or  optic  axis,  but  it  is  also  the  visual 
axis. 

Every  time  the  Javal  ophthalmometer,  or  any  other  oph- 
thalmometer, whose  disc  is  bordered  with  a  white  band,  is 


MUSCLES    EFFECTING    THEM.  3 

used,  the  anterior  pole  is  located,  nearly  always  to  the  nasal 
side  of  the  center  of  the  cornea.  The  corneal  meridians 
that  are  measured  by  the  ophthalmometer  are  those  lines 
which  cross  at  that  point  of  the  cornea  which  is  cut  by  the 
visual  axis;  for  this  axis  is  always  directed  to  the  center 
of  the  distal  opening  of  the  telescopic  tube.  On  looking 
above  the  tube,  while  the  patient  looks  into  the  center,  the 
operator  may  find  the  center  of  the  reflected  disc  and  the 
corneal  center  the  same ;  but  as  a  rule  the  center  of  the  re- 
flected disc  is  nasal-ward  from  the  corneal  center,  but 
wherever  it  is,  there  is  the  anterior  pole.  The  ideal  eye, 
and  the  best  seeing  eye,  other  things  being  equal,  is  the  one 
whose  corneal  center  is  the  anterior  pole.  If  the  anterior 
pole  is  removed  more  than  5°  from  the  corneal  center  it  is 
not  possible  for  such  an  eye  to  have  perfect  vision  for  the 
reason  that  the  rays  of  light  cannot  be  perfectly  focused 
on  the  macula.  The  best  refracted  rays  are  in  that  cone 
of  light  whose  axial  ray  cuts  the  corneal  center.  Inciden- 
tally it  may  be  suggested  that  a  displaced  anterior  pole  ac- 
counts for  the  fact  that,  in  most  cases,  the  ophthalmometer 
shows  an  excess  of  curvature  of  the  vertical  meridian, 
amounting  usually  to  .50  D  when  the  astigmatism  is  accord- 
ing to  the  rule,  making  it  necessary  to  take  .50  D  from  the 
cylinder.  The  same  reasoning  accounts  for  the  fact  that, 
in  astigmatism  against  the  rule  .50  D  must  be  added  to  the 
cylinder  indicated  by  the  ophthalmometer.     In  any  case  it 


4  OCULAR   ROTATIONS   AND   THE 

is  the  vertical  corneo-retinal  meridian  which  is  measured. 
When  this  coincides  with  the  curve  that  lies  in  the  vertical 
plane  which  cuts  the  center  of  the  cornea,  there  will  be 
nothing  to  add  to,  or  subtract  from,  the  ophthalmometer 
reading;  when  it  lies  in  the  plane  a  few  degrees  removed 
from  the  vertical  plane  which  cuts  the  center  of  the  cornea, 
whether  to  the  nasal  or  temporal  side,  there  must  be,  in 
astigmatism  against  the  rule,  an  addition  to  the  ophthalmo- 
meter reading;  likewise  there  must  be,  in  astigmatism  ac- 
cording to  the  rule,  a  subtraction  from  the  ophthalmometer 
reading.  The  addition  in  the  one  case  and  the  subtraction 
in  the  other  case  vary,  as  to  the  amount,  with  the  distance 
the  true  anterior  pole  is  from  the  center  of  the  corneal  curve. 
The  horizontal  corneo-retinal  meridian  has  lying  in  it,  prac- 
tically always,  both  the  anterior  pole  and  the  center  of  the 
cornea,  howsoever  widely  these  two  points  may  be  sep- 
arated. It  is  also  wrell  known  that  neither  addition  to,  nor 
subtraction  from,  the  ophthalmometer  reading  is  necessary 
in  astigmatism  in  which  one  principal  corneo-retinal  me- 
ridian is  at  45°  and  the  other  at  135°,  for  the  one  meridian 
misses  the  center  of  the  corneal  curve  to  the  same  extent 
as  does  the  other,  hence  an  error  in  the  measurement  of 
the  one  meridian  is  the  same  in  kind  and  quantity  as  the 
error  in  the  measurement  of  the  other.  To  make  plainer 
the  error  in  measurement  of  the  vertical  corneo-retinal  me- 
ridian when  the  anterior  pole  is  5°  nasal-ward  from  the  cor- 


MUSCLES   EFFECTING   THEM.  5 

neal  center,  two  vertical  planes  forming  an  angle  of  5° 
should  be  constructed,  the  one  cutting  the  corneal  center, 
the  other  cutting  the  anterior  pole,  the  center  of  rotation 
lying  in  both  planes.  In  the  latter  will  lie  the  vertical  cor- 
neo-retinal  meridian,  and  in  the  other  will  almost  lie  the 
corneal  refraction  curve  which  cuts  the  center  of  the  cornea. 
The  radius  of  the  former  corneal  curve  is  shorter  than  the 
radius  of  the  latter,  hence  the  difference  in  the  measure- 
ment of  the  two  by  the  reflected  images  of  the  mires.  The 
refraction  of  the  corneal  surface  is  by  the  curved  lines 
whose  planes  all  cross  each  other  at  the  center  of  the  cornea, 
which,  as  already  shown,  may  or  may  not  be  the  anterior 
pole.  These  lines  should  be  called  the  corneal  refraction 
curves,  and  not  the  corneal  meridians,  to  avoid  confound- 
ing them  with  the  corneo-retinal  meridians. 

With  the  poles  and  the  axis  correctly  located,  the  true 
equatorial  plane  is  easily  constructed.  Since  the  equator 
is  a  line  equally  distant,  at  all  points,  from  the  two  poles, 
the  equatorial  plane  must  be  at  right  angles  to  the  axis, 
and  must  cut  it  at  its  central  point.  This  point  in  the  eye 
is  the  center  of  rotation. 

Whenever  the  eye  is  moved  from  one  point  of  view  to  an- 
other, it  takes  the  shortest  course,  that  the  movement  may 
be  accomplished  in  the  quickest  time,  and  at  the  least  ex- 
pense of  nerve  force  and  muscle  energy.  This  being  true 
it  is  clear  that  the  visual  axis  has  moved  in  a  plane  common 


6  OCULAR   ROTATIONS   AND   THE 

to  both  its  first  and  second  positions.  Helmholtz's  rule  for 
locating  the  axis  of  any  possible  ocular  rotation,  whether  by 
the  action  of  one  muscle  or  by  the  combined  action  of  two 
or  more  muscles,  must  forever  stand,  for  it  is  true.  This 
is  his  simple  rule :  "The  axis  of  any  rotation  of  the  eye  is 
a  line  passing  through  the  center  of  rotation,  at  right  angles 
to  the  plane  common  to  both  the  primary  and  secondary 
positions  of  the  visual  axis."  It  needs  no  further  argu- 
ment to  show  that  the  axis  of  every  ocular  rotation  must 
lie  in  the  true  equatorial  plane. 

Listing's  plane  would  never  have  been  constructed  if  the 
error  had  not  previously  been  made  in  first  locating  the  an- 
terior pole  in  the  center  of  the  corneal  curve,  and  then  find- 
ing the  posterior  pole  by  extending  a  line  from  the  supposed 
anterior  pole,  back  through  the  center  of  rotation,  to  the 
retina,  and  naming  it  the  antero-posterior,  or  optic,  axis. 
The  circle  equally  distant  from  these  two  so-called  poles 
could  not  coincide  with  the  true  equator  except  in  an  ideal 
eye — one  whose  visual  axis  cuts  the  center  of  the  cornea — 
but  such  an  eye  is  rarely  found. 

The  confusion  arising  from  wrongly  locating  the  poles 
led  Listing  to  construct  his  plane,  a  fixed  vertical  plane,  cut- 
ting the  centers  of  rotation  of  the  two  eyes,  and  then  to 
declare  that  the  axes  of  all  ocular  rotations  lie  in  this  plane. 
Helmholtz  accepted  the  plane  but  rejected,  in  part,  the  teach- 
ing of  Listing  as  to  the  location  of  the  axes  of  rotations. 


MUSCLES   EFFECTING   THEM.  7 

Helmholtz  accepted  the  teaching  that  the  axis  of  a  rotation 
from  the  primary  position  to  a  secondary  position,  or  vice 
versa,  lies  in  Listing's  plane,  and  in  this  he  was  correct; 
but  he  claimed  that  the  axis  of  a  rotation  from  one  second- 
ary position  to  another  secondary  position  must  lie  in  a 
plane  bisecting  the  angle  between  the  Listing  plane  and  the 
so-called  equatorial  plane.  The  so-called  equatorial  plane 
is  at  right  angles  to  that  axis  whose  anterior  pole  is  the 
center  of  the  corneal  curve;  the  real  equatorial  plane  is  at 
right  angles  to  that  axis  whose  posterior  pole  is  the  fovea 
centralis.  If  the  angle  between  the  true  axis  (the  visual 
axis)  and  the  false  axis  (the  so-called  optic  axis)  is  5°, 
the  angle  formed  by  the  intersection  of  the  true  equatorial 
plane  and  the  false  equatorial  plane  must  be  5°.  In  only 
a  limited  number  of  rotations  from  one  secondary  position 
to  another  secondary  position  would  the  true  equatorial 
plane  bisect  the  angle  formed  by  the  Listing  plane  and  the 
false  equatorial  plane.  Helmholtz  was  entirely  correct  in 
teaching  that  the  axis  of  rotation  from  the  primary  to  any 
secondary  position  lies  in  the  Listing  plane ;  he  was  also  en- 
tirely correct  when  he  taught  that  the  axis  of  a  rotation 
from  one  secondary  position  to  any  other  secondary  position 
does  not  lie  in  the  Listing  plane ;  but  he  was  incorrect  in  his 
teaching  that  the  axes  of  rotations  from  secondary  positions 
to  secondary  positions  must  always  lie  in  a  plane  bisecting 
the  angle  formed  by  the  so-called  equatorial  plane  and  the 


8  OCULAR   ROTATIONS   AND   THE 

Listing  plane.  He  was  near  the  truth  and  yet  did  not  grasp 
it,  else  he  would  have  taught  that  every  rotation,  whether 
from  the  primary  position  to  a  secondary  position,  from  a 
secondary  position  back  to  the  primary  position,  or  from 
one  secondary  position  to  any  other  secondary  position, 
must  have  its  axis  in  that  movable  plane  which  is  always  at 
right  angles  to  the  visual  axis.  As  has  been  shown,  this  is 
the  true  equatorial  plane.  When  the  axis  is  in  the  Listing 
plane  it  is  also  in  the  equatorial  plane ;  when  the  axis  is  not 
in  the  Listing  plane  it  is,  never-the-less,  in  the  equatorial 
plane.  Therefore  the  Listing  plane  has  no  place  in  the 
study  of  ocular  rotations. 

The  Listing  plane  is  of  no  value  as  a  plane  of  reference, 
for  the  only  two  reference  planes  needed  are  the  median 
vertical  and  the  horizontal  fixed  planes  of  the  head. 

The  ocular  muscles  and  their  innervation  centers  work  in 
the  interest  of  binocular  single  vision  and  correct  orienta- 
tion. For  the  accomplishment  of  these  two  purposes  the 
muscles  of  the  eyes  are  concerned  only  with  the  visual  axes 
and  the  vertical  axes.  In  the  final  result  of  their  action, 
the  recti  muscles  are  concerned  only  with  the  visual  axes, 
while  the  oblique  muscles  are  concerned  only  with  the  ver- 
tical axes.  The  law  governing  all  possible  ocular  rotations 
may  be  thus  stated:  "The  recti  muscles  must  control  the 
visual  axes,  the  superior  and  inferior  recti  keeping  them  al- 
ways in  the  same  plane,  the  external  and  internal  recti 


MUSCLES   EFFECTING   THEM.  9 

making  them  intersect  at  the  point  of  fixation.  The  obliques 
must  keep  the  vertical  axes  parallel  with  each  other  and 
with  the  median  vertical  plane  of  the  head." 

The  law  of  rotation  of  a  single  eye  may  be  stated  as  fol- 
lows: "The  axis  of  every  possible  rotation,  whether  effected 
by  the  action  of  one  muscle  or  by  the  combined  action  of 
two  or  more  muscles,  must  lie  in  the  movable  equatorial 
plane  and  must  always  be  fixed  at  right  angles  to  the  plane 
through  which  the  visual  axis  moves  from  the  first  to  the 
second  position." 

Each  of  the  extrinsic  ocular  muscles  has  its  individual 
plane  of  action,  and  if  each  muscle  acted  by  itself,  the  visual 
axis  would  move  in  this  plane,  the  axis  of  rotation  being  at 
right  angles  to  it.  The  plane  of  rotation  of  an  individual 
muscle  must  pass  through  three  points,  viz.:  the  center  of 
the  origin  and  the  center  of  insertion  of  the  muscle,  bisect- 
ing it  from  end  to  end,  and  the  third  point  is  the  center  of 
rotation  of  the  eye.  Only  the  lateral  recti  muscles  with  ideal 
origins  and  insertions,  their  planes  coinciding  with  the  hori- 
zontal plane  of  the  eye,  can  act  alone  and  obey  the  law  of 
ocular  rotations.  A  too  high  or  a  too  low  insertion  of  an 
externus  or  an  internus  would  tilt  the  muscle  plane  so  that 
it  could  not  coincide  with  any  meridian  of  the  eye,  and 
therefore  its  axis  of  rotation  could  not  be  in  the  equatorial 
plane.  With  such  faulty  attachment  the  internus  unaided 
cannot  rotate  the  eye  directly  in.     The  muscle  plane  of  a 


10  OCULAR   ROTATIONS   AND   THE 

superior  or  inferior  rectus  does  not  coincide  with  the  plane 
of  any  corneo-retinal  meridian,  therefore  the  imperious  law 
of  ocular  rotations  will  not  allow  either  of  these  muscles  to 
act  by  itself,  since  the  axis  of  such  a  rotation  could  not  lie 
in  the  equatorial  plane.  The  same  is  true  of  the  obliques.  In 
ideally  attached  muscles,  rotation  directly  out  is  effected  by 
one  muscle,  the  externus;  rotation  directly  in  is  accom- 
plished by  one  muscle,  the  internus;  rotation  directly  up 
is  effected  by  two  muscles,  the  superior  rectus  and  the  in- 
ferior oblique;  rotation  directly  down  is  accomplished  by 
two  muscles,  the  inferior  rectus  and  the  superior  oblique. 
Rotations  obliquely  up  or  down  in  any  plane  between  90° 
and  180°  is  accomplished  by  three  muscles,  two  recti  and 
one  oblique,  and,  if  it  be  the  right  eye  and  the  rotation  is 
up  and  to  the  right,  these  three  muscles  are  the  superior 
and  external  recti  and  the  superior  oblique;  and  if  down 
and  to  the  left,  they  are  the  inferior  and  internal  recti  and 
the  superior  oblique;  but  if  it  be  the  left  eye  rotating  in 
either  of  these  directions  these  muscles  are,  respectively,  the 
superior  and  internal  recti  and  the  inferior  oblique,  and 
the  inferior  and  external  recti  and  inferior  oblique.  Rota- 
tions obliquely  up  or  down  in  any  plane  between  zero  and 
90°,  this  plane  being  up  and  to  the  left  and  down  and  to 
the  right,  is  accomplished  by  three  muscles,  two  recti  and 
one  oblique.  If  it  be  the  right  eye  and  the  rotation  is  up 
these  three  muscles  are  the  superior  and  internal  recti  and 


MUSCLES   EFFECTING   THEM.  11 

the  inferior  oblique ;  and  if  down,  they  are  the  inferior  and 
external  recti  and  inferior  oblique.  But  if  it  be  the  left  eye 
and  the  rotation  is  up,  these  three  muscles  are  the  superior 
and  external  recti  and  the  superior  oblique,  and  if  down 
they  are  the  inferior  and  internal  recti  and  the  superior 
oblique. 

Whenever  the  plane  of  rotation  is  oblique  the  visual  axis 
could  not  move  in  it  without  torsioning  the  eye,  if  this  evil 
effect  were  not  counteracted  by  an  oblique  muscle.  The 
work  accomplished  by  the  oblique  muscle,  in  an  oblique 
rotation,  is  in  maintaining  parallelism  between  the  vertical 
axis  of  the  eye  and  the  median  plane  of  the  head.  When 
the  two  planes  of  binocular  rotations  are  between  90°  and 
180°,  whether  the  visual  axes  are  made  to  sweep  above  or 
below  the  fixed  horizontal  plane  of  the  head,  the  torsional 
tendency  is  such  as  would  make  both  vertical  axes  incline 
to  the  right;  but  this,  in  the  right  eye,  is' prevented  by  the 
superior  oblique,  while  in  the  left  eye  it  is  prevented  by  the 
inferior  oblique.  When  the  two  planes  of  binocular  rota- 
tions are  between  zero  and  90°,  whether  the  visual  axes  are 
made  to  move  above  or  below  the  fixed  horizontal  plane  of 
the  head,  the  torsional  tendency  is  such  as  would  make  both 
vertical  axes  incline  to  the  left;  but  this,  in  the  right  eye, 
is  prevented  by  the  inferior  oblique,  while  in  the  left  eye,  it 
is  prevented  by  the  superior  oblique. 

The  supreme  law  of  binocular  rotations  is  the  law  of  cor- 


12  OCULAR   ROTATIONS   AND    THE 

responding  retinal  points.  To  so  relate  the  two  retinas 
that  they  may  receive,  on  corresponding  parts,  the  two 
images  of  the  single  object,  the  superior  and  inferior  recti 
must  keep  the  two  visual  axes  in  the  same  plane;  the  in- 
ternal and  external  recti  must  converge  these  axes  at  the 
point  of  fixation;  and  the  obliques  must  keep  the  vertical 
axes  parallel  with  the  median  plane  of  the  head.  These  con- 
ditions must  exist  whether  the  object  of  view  is  immediately 
in  front,  or  directly  above  or  below  the  extended  horizontal 
plane  of  the  head,  or  directly  to  the  right  or  left  of  the  ex- 
tended median  plane  of  the  head,  or  in  any  oblique  position. 
It  is  no  less  true  that  these  conditions  must  be  maintained 
when  the  two  eyes  are  being  rotated  from  any  one  point 
to  any  other  point  in  the  field  of  vision.  That  this  may  be 
true  every  rotation  plane  must  be  a  meridional  plane  ex- 
tended, and  every  axis  of  rotation  must  lie  in  the  equatorial 
plane.  Every  rotation  plane  is  a  fixed  plane,  for  in  it  lie 
three  fixed  points,  viz.:  the  first  and  second  points  of  view 
and  the  center  of  rotation.  If,  in  oblique  rotations,  the 
eyes  were  allowed  to  tort,  as  taught  by  Listing,  the  rota- 
tion plane,  which  is  an  extended  meridional  plane,  would 
also  tort,  therefore  it  could  not  be  a  fixed  plane. 

Correct  orientation,  as  well  as  binocular  single  vision,  de- 
mands that  ocular  rotations  shall  be  in  meridional  planes, 
and  that  the  axes  of  all  rotations  shall  lie  in  the  equatorial 
plane. 


MUSCLES   EFFECTING   THEM.  13 

If  the  eye  can  be  rotated  in  a  meridional  plane  by  a  mus- 
cle, only  that  one  muscle  will  be  called  into  action;  if  the 
united  action  of  two  muscles  will  cause  an  eye  to  rotate  in 
a  meridional  plane,  then  only  these  two  muscles  will  be  ex- 
cited into  activity.  All  rotations  in  oblique  meridional 
planes  are  effected  by  the  conjoined  action  of  three  muscles, 
and  only  three. 

Every  muscle  has  two  properties,  viz. :  tonicity  and  con- 
tractility. A  muscle,  in  a  perfect  state  of  rest,  manifests 
its  tonicity;  a  muscle  excited  by  receiving  a  charge  of  neu- 
ricity,  exhibits  its  power  of  contractility.  Tonicity  may  be 
termed  latent  power;  contractility  is  manifest  power.  To- 
nicity is  rest;  contractility  is  action.  Alternate  rest  and 
action  tend  to  preserve  the  healthfulness  of  muscles.  Too 
much  contraction  of  a  muscle  (overwork)  impairs  its  tonic- 
ity; too  much  rest  enfeebles  the  contractile  power  of  a 
muscle. 

The  muscles  of  the  two  eyes  must  work  in  harmony  and 
with  mathematical  exactness.  They  work  in  pairs,  and  one 
muscle  of  every  pair  is  connected  with  each  eye.  To  effect 
the  right  rotation  of  the  eyes,  the  right  externus  and  left 
internus  constitute  a  pair;  in  the  left  sweep  of  the  eyes, 
the  left  externus  and  the  right  internus  constitute  a  pair; 
in  the  act  of  convergence  the  two  interni  constitute  a  pair. 
In  the  upward  sweep  of  the  eyes  the  two  superior  recti  con- 
stitute a  pair,  and  in  this  they  are  aided  by  the  two  inferior 


14  OCULAR   ROTATIONS   AND   THE 

obliques  constituting  another  pair.  In  the  downward  sweep 
of  the  eyes  the  two  inferior  recti  constitute  a  pair,  and  as 
helpers  in  this  movement  the  two  superior  obliques  consti- 
tute a  pair.  In  oblique  rotations  up  and  to  the  right,  the 
right  externus  and  left  internus  constitute  a  pair,  the  two 
superior  recti  constitute  a  pair,  and  the  right  superior 
oblique  and  the  left  inferior  oblique  constitute  another  pair. 
In  rotations  down  and  to  the  left,  the  left  externus  and  the 
right  internus  make  one  pair,  the  two  inferior  recti  make 
one  pair,  and  the  right  superior  oblique  and  left  inferior 
oblique  make  another  pair.  In  oblique  rotations  up  and  to 
the  left,  the  left  externus  and  right  internus  make  one  pair, 
the  two  superior  recti  make  one  pair,  and  the  left  superior 
oblique  and  right  inferior  oblique  make  another  pair.  In 
oblique  rotations  down  and  to  the  right,  the  right  externus 
and  the  left  internus  make  one  pair,  the  two  inferior  recti 
make  one  pair,  and  the  left  superior  oblique  and  right  in- 
ferior oblique  make  another  pair.  These  various  rotations 
are  accomplished  with  the  greatest  ease  if  the  muscles  con- 
cerned have  their  normal  tonicity — if  there  is  orthophoria. 

Tonicity. 

The  study  of  tonicity  of  the  muscles  must  likewise  be 
made  in  pairs,  but  the  two  muscles  constituting  any  pair  be- 
long to  the  same  eye.  With  the  head  in  the  primary  po- 
sition, the  superior  and  inferior  recti  possessed  of  ideal 


MUSCLES   EFFECTING   THEM.  15 

tonicity  would  cause  the  visual  axis  to  lie  in  the  extended 
horizontal  plane  of  the  head,  when  unexcited  by  neuricity 
from  either  the  cortical  or  basal  centers  controlling  them. 
The  internal  and  external  recti  whose  tonicity  is  ideal  would 
place  the  visual  axis  parallel  with  the  extended  median  plane 
of  the  head,  when  uninfluenced  by  neuricity  from  either  cor- 
tical or  basal  centers.  The  superior  and  inferior  obliques 
with  ideal  tonicity  would  make  the  vertical  axis  parallel 
with  the  median  plane  of  the  head  although  uninfluenced 
by  neuricity  from  either  basal  or  cortical  centers.  These 
statements  being  true,  it  becomes  self-evident  that  if  the 
tonicity  of  a  superior  rectus  be  greater  than  that  of  the  in- 
ferior rectus  of  the  same  eye  (hyperphoria) ,  the  visual  axis 
would  be  elevated  above  the  extended  horizontal  plane  of 
the  head,  and  if  the  tonicity  of  the  inferior  rectus  be  great- 
er than  that  of  the  superior  rectus  of  the  same  eye  (cata- 
phoria)  the  visual  axis  would  be  depressed  below  the  ex- 
tended horizontal  plane  of  the  head.  In  either  case,  that 
there  may  be  binocular  single  vision,  the  muscle  with  less 
tonicity  must  receive  a  certain  amount  of  neuricity  from  its 
proper  basal  center,  that  contractility  may  be  made  to  sup- 
plement tonicity  and  thus  make  the  weaker  muscle  evenly 
balance  the  tonicity  of  the  stronger  muscle. 

In  like  manner  it  becomes  evident  that,  if  the  tonicity  of 
the  externus  is  greater  than  that  of  the  internus  of  the  same 
eye    (exophoria)    the  visual  axis  would  be  made  to  point 


16  OCULAR   ROTATIONS   AND   THE 

from  the  extended  median  plane  of  the  head;  and  if  the 
tonicity  of  an  interims  is  greater  than  that  of  the  externus 
of  the  same  eye  (esophoria),  the  visual  axis  would  be 
made  to  point  towards  the  extended  median  plane  of  the 
head.  In  either  case,  that  there  may  be  binocular  single 
vision,  the  muscle  wanting  in  tonicity  must  receive  a  definite 
quantity  of  neuricity  from  its  proper  basal  center,  that  con- 
tractility may  supplement  its  tonicity  and  thus  make  it 
equal,  in  power,  the  tonicity  of  the  stronger  muscle.  With 
the  visual  axis  lying  in  the  extended  horizontal  plane  and 
parallel  with  the  extended  median  plane  of  the  head,  the 
oblique  muscles,  if  equal  in  tonicity,  would  parallel  the 
vertical  axis  with  the  median  plane.  If  the  tonicity  of  the 
superior  oblique  should  be  greater  than  that  of  the  inferior 
oblique  of  the  same  eye  (minus  cyclophoria),  the  vertical 
axis  would  be  inclined  toward  the  median  plane  of  the  head ; 
if  the  inferior  oblique  should  have  the  greater  tonicity  (plus 
cyclophoria) ,  the  vertical  axis  would  deviate  from  the  ver- 
tical plane  of  the  head.  In  either  condition,  whether  the 
vision  is  monocular  or  binocular,  the  weaker  muscle  must 
receive  neuricity  from  its  proper  basal  center  that  contrac- 
tility may  be  excited  to  supplement  its  tonicity  in  the  work 
of  paralleling  the  vertical  axis  with  the  median  plane  of  the 
head. 

The  tonicity  of  the  recti  muscles  would  demand  but  little 
study  if  there  were  only  one  eye,  for  the  visual  axis  might 


MUSCLES   EFFECTING   THEM.  17 

form  any  angle  with  either  the  extended  vertical  or  horizon- 
tal planes  of  the  head  without  interference  with  orientation. 
A  posing  of  the  head,  therefore,  would  compensate  for  any 
difference  in  tonicity  between  the  members  of  either  pair  of 
recti  muscles,  in  persons  possessed  of  only  one  eye.  Unequal 
tonicity  of  the  obliques,  in  a  one-eyed  person,  cannot  be 
counteracted  so  easily  by  any  pose  of  the  head,  therefore  the 
demand  on  these  muscles  would  be  just  as  great  if  there 
were  only  one  eye  as  when  there  are  two.  Correct  orienta- 
tion depends  on  perfect  parallelism  of  the  vertical  axis  of 
the  eye  with  the  median  plane  of  the  head.  This  law  is  in- 
fringed only  in  the  interest  of  binocular  single  vision,  and 
then  only  in  cases  of  non-symmetric  oblique  astigmatism. 

In  binocular  vision  the  importance  of  the  study  of  the 
tonicity  of  the  ocular  muscles  cannot  be  over-estimated.  It 
is  easily  within  the  power  of  every  ophthalmic  surgeon  to 
become  a  master  in  this  study.  To  determine  the  tonicity 
of  either  the  recti  or  the  obliques,  care  must  be  exercised  to 
avoid,  as  far  as  possible,  a  flow  of  neuricity  from  any  cor- 
tical center,  and  that  all  basal  centers  shall  be  perfectly 
quiet.  In  well  balanced  emmetropic  eyes  there  is  no  activity 
of  either  cortical  or  basal  centers,  when  the  head  is  in  the 
primary  position,  the  visual  axes  lying  in  the  extended  hori- 
zontal plane  of  the  head  and  being  parallel  (or  practically 
so)  with  the  extended  median  plane  of  the  head.  When 
these  conditions  are  met,  and  the  two  eyes  are  heterophoric 


18  OCULAR   ROTATIONS   AND    THE 

but  emmetropic,  all  the  volitional  centers,  to  be  studied  fur- 
ther on,  must  be  free  from  any  demand  for  neuricity,  hence 
no  muscle  contraction  can  come  from  that  source.  It  only 
remains  to  put  at  rest  the  basal  centers  which  are  under 
the  control  of  the  fusion  faculty  of  the  mind.  This  is  done 
by  producing  insuperable  diplopia.  Fusion  having  been 
rendered  impossible  by  the  displacing  prism,  no  fusion  or 
basal  center  will  be  called  into  action,  hence  no  muscle  con- 
traction can  come  from  that  source. 

The  only  wholly  trustworthy  instrument  for  placing  the 
fusion  centers  at  rest,  and  detecting  and  measuring  errors 
of  tonicity  in  the  recti  muscles,  is  the  Monocular  Phorometer. 
The  displacing  prism  of  this  instrument  must  throw  the 
image  in  the  eye  before  which  it  stands,  entirely  outside 
the  retinal  fusion  area.  The  other  eye,  before  which  no 
part  of  the  instrument  is  placed,  must  fix  the  test  object 
seen  by  it,  and  the  test  object  must  be  so  related  to  this  eye 
that  its  visual  axis  and  the  object  shall  lie  in  the  extended 
horizontal  plane  of  the  head.  If  the  false  object  has  been 
displaced  laterally  and  the  superior  and  inferior  recti  of  the 
two  eyes  have  equal  tonicity,  the  false  and  the  true  objects 
will  be  in  the  same  horizontal  plane;  but  if  the  superior 
rectus  of  the  eye  under  test  has  greater  tonicity  than  its 
inferior  rectus  (hyperphoria),  the  false  object  will  be  seen 
lower  than  the  true  object.  The  rotary  prism  can  be  made 
to  lift  the  false  object  into  the  same  plane  with  the  true, 


MUSCLES.  EFFECTING    THEM.  19 

when  the  index  will  show  the  degree  of  the  error.  But  the 
amount  of  the  error  thus  measured  is  in  excess  of  the  true 
error,  as  can  be  easily  shown.  The  inferior  rectus  of  the 
fixing  eye  having  greater  tonicity  than  its  superior  rectus, 
the  two  muscles  in  a  state  of  rest  would  cause  the  visual 
axis  to  be  depressed.  To  bring  this  axis  into  the  horizontal 
plane  the  cortical  center  that  controls  the  upward  sweep 
of  the  eyes  must  be  excited  into  activity,  the  result  being  a 
contraction  of  both  superior  recti.  As  will  be  shown,  this 
center  sends  the  same  quantity  of  neuricity  to  one  of  these 
muscles  that  it  sends  to  the  other.  The  greater  tonicity  of 
the  superior  rectus  of  the  eye  under  test  would  elevate  its 
visual  axis  above  the  extended  horizontal  plane  of  the  head, 
but  the  contractility  excited  by  the  neuricity  sent  equally 
to  the  two  superior  recti,  makes  the  visual  axis  of  this  eye 
move  faster  and  rise  higher  than  the  other,  and  throws  the 
false  object  correspondingly  lower.  Thus  would  be  shown 
a  greater  deviation  tendency  than  really  exists.  This  ex- 
plains what  experience  has  taught,  that  a  full  prismatic  cor- 
rection should  not  be  given  when  a  vertical  deviation  tend- 
ency is  to  be  treated  by  a  prism  in  position  of  rest. 

In  testing  the  tonicity  of  the  external  and  internal  recti 
the  head  must  be  in  the  primary  position,  and  the  test  object 
should  be  at  practical  infinity  and  in  the  line  of  intersection 
of  the  extended  median  and  horizontal  fixed  planes  of  the 
head.     The  displacing  prism  with  its  base  up  before  one 


20  OCULAR   ROTATIONS   AND   THE 

eye  should  be  sufficiently  strong  to  throw  the  image  of  the 
test  object  in  that  eye  entirely  outside  the  fusion  area,  so 
as  to  place  in  absolute  rest  the  basal  or  fusion  centers.  If 
the  lateral  recti  are  possessed  of  equal  tonicity,  the  false 
object  will  be  below  the  true  but  in  the  same  vertical  plane; 
but  if  the  tonicity  of  the  interni  is  greater  than  the  tonicity 
of  the  externi  (esophoria),  the  false  object,  if  seen  by  the 
left  eye,  will  be  to  the  left  of  this  plane.  The  rotary  prism 
measures  the  amount  of  this  deviation  by  bringing  the  false 
object  directly  under  the  true.  The  measurement,  however, 
is  in  excess  of  the  true  error  for  this  reason:  the  internal 
rectus  of  the  fixing  eye  (in  this  instance  the  right  eye) 
being  possessed  of  greater  tonicity  than  its  externus,  the 
restful  state  (tonicity)  of  these  muscles  would  make  the 
visual  axis  point  towards  the  extended  median  plane.  The 
fourth  cortical  center,  which  controls  the  right  sweep  of 
the  eyes,  must  send  neuricity  to  the  right  externus  so  as 
to  add  contractility  to  its  tonicity  and  thus  place  the  visual 
axis  parallel  with  the  median  plane.  The  fourth  cortical 
center,  thus  excited,  sends  an  equal  amount  of  neuricity  to 
the  left  internus,  and  this  muscle  having  greater  tonicity 
than  the  right  externus,  responds  more  powerfully  and  ro- 
tates its  eye  faster  and  further  under  the  equal  stimulus, 
and  thus  throws  the  false  object  correspondingly  too  far 
from  the  median  plane.  To  avoid  this  error  in  measure- 
ment the  test  object  should  be  on  the  visual  axis  of  the  fixing 


MUSCLES   EFFECTING   THEM.  21 

eye,  its  lateral  recti  being  in  the  restful  state,  but  it  would 
be  impossible  to  determine  this  position  in  any  case.  This 
error  in  measurement,  when  the  head  is  in  the  primary  po- 
sition and  the  test  object  properly  placed,  may  be  much  or 
little,  depending  on  the  difference  in  tonicity  of  the  two 
muscles  controlled  by  the  excited  cortical  center. 

With  the  head  in  the  primary  position,  the  test  object  in 
the  line  of  intersection  of  the  extended  median  and  hori- 
zontal planes  of  the  head  and  at  practical  infinity  (thirty 
feet  would  be  better  than  twenty),  with  the  false  image 
thrown  entirely  outside  the  retinal  fusion  area,  and  the  free 
eye  used  for  fixation,  the  measurement  of  any  deviation  will 
be  more  or  less  in  excess  of  the  true  error,  but  this  meas- 
urement will  not  vary  from  day  to  day,  except  under  treat- 
ment. Non-observance  of  these  details  accounts  fully  for 
the  complaint  of  some  that  the  measurements  of  muscle 
errors  vary  from  time  to  time.  The  binocular  phorometer 
may  be  another  cause  of  variation  in  measurements. 

Tonicity  of  the  Obliques. — The  test,  or  tests,  for  deter- 
mining the  tonicity  of  the  obliques  should  be  made  when 
both  the  head  and  eyes  are  in  their  primary  positions.  The 
test  object  may  be  a  horizontal  line  on  a  black  board,  twenty 
feet  distant,  or  a  horizontal  line  on  a  card  to  be  held  at  the 
reading  distance.  The  means  for  making  this  test  may  be 
a  single  prism  of  6  degrees  taken  from  the  test  case.  This 
prism  should  be  placed,  base  up,  before  one  eye.     Fixing  the 


22  OCULAR   ROTATIONS   AND   THE 

real  line  with  the  other  eye,  the  image  of  the  line  in  the 
eye  under  test  will  lie  entirely  above  the  retinal  fusion  area, 
and  no  attempt  at  fusion  will  be  made.  The  non-fixing  eye 
— the  one  under  test — will  assume  at  once  that  position  in 
its  orbit  in  which  the  tonicity  of  the  recti  and  the  obliques 
would  place  it.  If  the  obliques  of  this  eye  are  well  balanced, 
if  they  have  equal  tonicity,  the  false  line  will  be  parallel 
with  the  true  one;  if  the  superior  oblique  has  less  tonicity 
than  the  inferior,  the  false  line  will  dip  towards  the  opposite 
side,  the  two  lines  appearing  to  be  wider  apart  at  the  ends 
corresponding  to  the  eye  not  under  test;  if  the  inferior 
oblique  has  less  tonicity  than  the  superior,  the  false  line  will 
dip  towards  the  corresponding  side,  the  lines  appearing  to 
be  closer  together  at  the  ends  corresponding  to  the  eye  not 
under  test.  If  the  line  seen  by  the  eye  not  under  test  is 
constantly  fixed,  it  will  remain  horizontal,  however  much 
the  false  line  may  incline,  and  for  the  reason  that  the  image 
of  the  former  lies  wholly  in  the  retinal  fusion  area,  thus 
compelling  the  obliques  of  this  eye,  though  unequal  in  tonic- 
ity, to  parallel  the  vertical  axis  with  the  median  plane  of 
the  head.  Under  the  single  prism  test,  cyclophoria  can  be 
detected  easily  and  its  kind  determined,  but  its  quantity  can- 
not be  measured. 

The  use  of  the  Maddox  double  prism  is  neither  easier  nor 
more  accurate  than  that  of  the  single  prism.  The  double 
prism  is  of  interest,  however,  for  the  reason  that  it  was  the 


MUSCLES   EFFECTING   THEM.  23 

means  that  resulted  in  the  discovery  of  cyclophoria  in 
1890,  just  fifteen  years  ago.  The  author  made  his  first  pub- 
lication on  unequal  tonicity  of  the  obliques  in  the  Archives 
of  Ophthalmology,  January,  1891,  under  the  caption,  "In- 
sufficiency of  the  Obliques."  The  accompanying  figures 
1,  2,  3  and  4  were  used  to  illustrate  that  paper,  and  the  fol- 
lowing language  was  used  in  the  text:  "Place  a  double 
prism,  axis  vertical,  before  one  eye,  the  other  for  the  mo- 
ment being  covered,  and  ask  the  patient  to  look  at  a  hori- 
zontal line  on  a  card  held  sixteen  inches  away.  The  effect 
of  the  double  prism  (each  6°)  is  to  make  the  line  appear  to 
be  two,  each  parallel  with  the  other.  The  other  eye  is  now 
uncovered,  and  a  third  line  is  seen  between  the  other  two, 
with  which  it  should  be  perfectly  parallel. 

"If  there  is  a  want  of  harmony  on  the  part  of  the  oblique 
muscles  [unequal  tonicity],  this  test  will  show  it  at  once  in 
a  want  of  parallelism  of  the  middle  line  with  the  two  other 
lines,  the  right  end  of  the  middle  line  pointing  towards  the 
bottom  line  and  the  left  end  towards  the  top  line,  or  vice 
versa,  depending  on  the  nature  of  the  individual  case. 

"Consider  the  eye  before  which  no  prism  is  held  as  the  one 
under  test.  With  the  double  prism  before  the  right  eye,  the 
patient  is  asked  about  the  position  and  direction  of  the  mid- 
dle line.  It  may  be  nearer  the  bottom  line,  thus  showing 
left  hyperphoria;  or,  again,  it  may  extend  further  to  the 
right  than  the  other  two,  and  not  so  far  to  the  left,  thus 


24  OCULAR   ROTATIONS   AND   THE 

showing  exophoria;  or,  vice  versa,  showing  esophoria.  If 
the  right  ends  of  the  middle  and  bottom  lines  converge  while 
the  left  ends  diverge,  the  superior  oblique  of  the  left  eye 
is  at  once  shown  to  be  in  a  state  of  underaction  [wanting  in 
tonicity].  Figure  1  represents  such  a  test  of  the  left  eye; 
Figure  2  shows  a  test  of  the  left  eye  where  the  inferior 
oblique  is  the  too  weak  muscle;  Figure  3  represents  a  test 
of  the  right  eye,  the  loss  of  parallelism  between  the  lines 
being  due  to  underaction  of  its  superior  oblique;  Figure 


Fig.  i.  Fig.  *. 

4,  the  same  condition  of  the  inferior  oblique  of  the  right 
eye." 

The  changes  that  the  author  would  make  in  the  language 
then  used,  if  he  were  now  speaking,  for  the  first  time,  of 
the  double  prism  test  for  determining  the  tonicity  of  the 
obliques,  would  be  to  substitute  "cyclophoria"  for  "insuffi- 
ciency of  the  obliques,"  "wanting  in  tonicity"  for  "under- 
action." He  would  also  emphasize  the  importance  of  fixing 
either  the  top  or  the  bottom  line,  so  that  the  eye  seeing  the 
middle  line  may  assume  the  position  allowed  by  the  tonicity 
of  all  its  muscles.     As  with  the  single  prism,  so  with  the 


MUSCLES   EFFECTING   THEM.  25 

double  prism,  cyclophoria  can  be  detected  and  classified,  but 
cannot  be  measured. 

The  rotary  prism  can  do  only  what  can  be  done  by  the 
single  and  double  prisms — that  is,  detect  and  classify  cyclo- 
phoria without  measuring  the  quantity.  To  make  the  test 
with  the  rotary  prism  it  should  be  adjusted  as  for  taking 
sub-  and  superduction.  Rotating  it  up  or  down,  beyond  the 
point  of  possible  fusion,  the  test  line  becomes  double.  The 
eye  seeing  the  true  line  should  be  the  fixing  eye,  as  in  the 


Fig.  3.  Fig.  4. 

test  with  the  single  prism.  If  the  tonicity  of  the  obliques  is 
normal  the  two  lines  will  be  parallel ;  if  the  superior  obliques 
are  wanting  in  tonicity  the  false  line  will  dip  towards  the 
opposite  side;  if  the  inferior  obliques  are  wanting  in  tonic- 
ity the  false  line  will  dip  towards  the  corresponding  side. 
Revolving  the  rotary  prism  towards  zero  will  make  the  two 
lines  approach  and  finally  fuse.  If  the  false  image  is  below 
and  is  seen  by  the  right  eye,  as  the  rotary  prism  is  moved 
toward  zero  the  right  ends  of  the  lines  will  fuse  first  in  plus 
cyclophoria,  and  the  left  ends  will  fuse  first  if  there  is  minus 
cyclophoria.     If  there  is  no  cyclophoria  the  two  lines  will 


26  OCULAR   ROTATIONS   AND   THE 

fuse  throughout  their  entire  length  at  the  same  moment. 
The  convenience  with  which  the  rotary  prism  can  be  used 
makes  it  more  desirable  than  the  single  prism  from  the  trial 
case. 

The  cyclophorometer  will  detect,  classify  and  measure  cy- 
clophoria.  This  instrument  should  be  perfectly  leveled  and 
the  index  of  each  rod  must  stand  at  zero.  Behind  the  right 
rod  a  6°  prism  should  be  placed  base  up,  and  behind  the 
other  rod,  unless  it  be  a  red  one,  should  be  placed  a  plane 
red  glass.  The  room  should  be  made  dark,  and  the  test  ob- 
ject should  be  a  candle,  or  better  still,  a  point  of  light.  The 
left  or  fixing  eye  would  see  a  red  streak  of  light  perfectly 
horizontal,  and  the  right  eye  would  see  a  yellow  streak  of 
light  below  the  red  one.  The  ends  should  be  made 
even  by  the  adjustment  screw  and  then  the  patient  should 
be  asked  if  the  two  streaks  are  parallel,  as  they  would 
be  if  there  is  no  cyclophoria.  If  the  yellow  streak  dips 
towards  the  left  there  is  plus  cyclophoria.  The  divergence 
of  the  lines  to  the  left  is  corrected  by  revolving  the  disc 
before  the  right  eye,  in  the  upper  temporal  quadrant,*  suf- 
ficiently far  to  bring  the  false  streak  into  the  horizontal 
position,  hence  into  parallelism  with  the  red  or  true  streak 
of  light.  The  index,  pointing  to  a  degree  mark  on  the  scale, 
will  show  the  amount  of  plus  torsioning  that  has  occurred. 

*  The  cyclophorometer  as  now  made  has  the  scale  in  the  unper  semicircle.  In  the  first 
instruments  made  the  scale  was  in  the  lower  semicircle.  The  latter  is  the  one  spoken  of 
in  Ophthalmic  Myology. 


MUSCLES   EFFECTING   THEM.  2< 

This  application  of  the  Maddox  rod  was  first  made  by 
Dr.  Price,  Nashville,  in  1894.  The  discs  containing  the  rods 
were  shown  by  him  at  the  San  Francisco  meeting  of  the 
American  Medical  Association  in  that  year.  The  one  disc 
was  an  unmodified  Maddox  triple  rod,  but  behind  the  triple 
rod  in  the  other  disc  was  a  double  prism.  This  arrange- 
ment gave  three  streaks  of  light,  two  seen  by  one  eye  and 
one  by  the  other  eye.  The  two  disc  were  set  in  ordinary 
trial  frames  the  leveling  of  which  could  only  be  approxi- 
mated. It  was  soon  observed  that  two  streaks  of  light  were 
all  that  were  necessary,  hence  the  double  prism  combina- 
tion has  been  abandoned  and  a  single  prism  substituted. 
Out  of  the  Price  device  was  evolved  the  author's  cyclopho- 
rometer,  which  can  be  used  in  both  the  tonicity  and  the  duc- 
tion  tests  of  the  obliques. 

The  clinoscope  devised  by  Stevens  not  earlier  than  1896 
and  probably  not  until  1897,  is  capable  of  detecting,  classify- 
ing and  measuring  cyclophoria,  which  Stevens  is  better 
pleased  to  term  retinal  declination,  although  the  term  cyclo- 
phoria had  been  previously  given  us  by  Price  in  conformity 
with  the  Stevens  nomenclature  concerning  the  recti  mus- 
cles. The  tonicity  test  with  the  clinoscope  should  be  made, 
preferably,  by  using  the  two  opaque  discs  that  contain  each 
a  diameter.  These  discs  should  be  so  placed  at  the  distal 
end  of  the  tubes  that  the  lines  would  be  horizontal.  At  the 
proximal  end  of  one  tube  should  be  placed  a  6°  prism,  base 


28  OCULAR   ROTATIONS   AND    THE 

up.  The  one  line  would  be  thrown  so  far  below  the  other 
that  no  attempt  at  fusion  would  be  made.  If  the  indices 
now  stand  at  zero,  the  two  lines  should  be  parallel.  Fixing 
the  gaze  on  the  upper  line,  if  the  bottom  line  is  not  parallel 
with  it,  the  tube  showing  the  dipping  line  should  be  re- 
volved so  as  to  make  the  displaced  line  parallel  with  the 
other.  The  index  pointing  outward  would  show  plus  cyclo- 
phoria,  and  the  degree  mark  at  which  the  index  stands 
shows  the  quantity  of  the  error. 

The  factors  entering  into  the  causation  of  cyclophoria  are 
fully  set  forth  in  "Ophthalmic  Myology."  The  condition  is 
one  and  the  same  by  whatever  name  it  may  be  called,  wheth- 
er "insufficiency  of  the  obliques"  (Savage),  "cyclophoria" 
(Price),    "torsion"     (Maddox),    or    "retinal    declination" 

(Stevens). 

Contractility. 

There  are  three  tests  for  determining  the  contractility 
of  the  ocular  muscles.  The  first  is  for  measuring  the  vol- 
untary contraction  of  the  muscles  when  made  to  move  the 
eyes  in  either  of  the  four  cardinal  directions ;  the  second  is 
to  ascertain  the  power  of  convergence;  and  the  third  is  to 
find  the  fusion  power  of  a  muscle. 

Version. — The  muscular  power  that  turns  the  eyes  in 
either  of  the  four  cardinal  directions  is  volitional,  and  the 
neuricity  that  causes  the  contraction  of  the  muscles  con- 
cerned comes  from  centers  in  the  cortex  of  the  brain.     No 


MUSCLES   EFFECTING   THEM.  29 

better  name  could  be  given  this  power  than  "version,"  espe- 
cially since  it  so  easily  combines  with  prefixes  that  indicate 
the  direction  of  the  turning,  as  abversion,  adversion,  sub- 
version and  superversion.  If  the  internus  and  the  externus 
have  the  same  tonicity,  adversion  and  abversion  will  be 
equal ;  if  there  is  greater  tonicity  of  the  internus  than  there 
is  of  the  externus,  adversion  will  be  greater  than  abversion ; 
but  if  the  externus  has  an  excess  of  tonicity,  abversion  will 
be  greater  than  adversion.  The  normal  verting  power  of 
an  externus  or  an  internus  is  about  50°.  Normal  subver- 
sion and  superversion  is  also  about  50°  each,  though  super- 
version  is  given  by  most  authors  as  much  less,  usually  about 
33°.  This  low  superversion  is  probably  due  to  the  fact  that 
the  test  object  becomes  obstructed  by  the  over-arching  brow, 
and  thus  causes  the  eye  to  lose  the  stimulus  for  further  rota- 
tion. The  best  means  for  determining  the  verting  power  of 
a  muscle  is  the  Stevens  tropometer.  One  eye  should  be 
covered  while  the  other  is  under  test.  The  perimeter  may 
be  used,  but  its  use  is  neither  so  easy  nor  accurate  as  the 
tropometer.  In  using  the  tropometer  or  the  perimeter,  the 
verting  power  of  only  one  muscle  of  one  eye  is  studied  at  a 
time ;  and  in  this  study  it  is  better  to  use  the  terms  adversion 
and  abversion,  in  expressing  the  rotation  power  of  the  in- 
terni  and  externi,  than  to  say  right  version  and  left  version. 
It  must  be  remembered,  however,  that  the  center  sending 
forth  the  neuricity  that  causes  abversion  of  one  eye  causes, 


30  OCULAR  ROTATIONS   AND   THE 

at  the  same  moment,  adversion  of  the  other  eye,  the  latter 
being  equal  in  extent  and  rapidity  to  the  former,  if  the  lat- 
eral muscles  are  orthophoria. 

The  power  to  turn  the  two  eyes  in  the  same  direction,  at 
will,  is  given  us,  that  the  point  of  view  may  be  changed,  in 
a  large  part  of  the  field  of  vision,  without  moving  the  head 
or  body.  The  centers  effecting  these  rotations  do  not  exist 
in  the  interest  of  binocular  single  vision  in  the  sense  that 
they  are  presided  over  by  the  fusion  faculty  of  the  mind, 
for,  as  already  stated,  they  are  volitional  centers.  Each 
center  influences  equally  two  muscles,  one  belonging  to 
each  eye,  but  not  always  with  the  same  result,  the  difference 
in  result  depending  on  a  difference  in  the  tonicity  of  the  two 
muscles  concerned.  If  the  two  muscles  are  orthophoria — 
equal  in  tonicity — the  center  calling  them  into  action  will 
effect  the  rotation  without  diplopia  or  a  tendency  towards 
its  production.  If  the  two  muscles  are  heterophoric — un- 
equal in  tonicity — the  center  exciting  them  would  cause  the 
stronger  muscle  to  rotate  its  eye  further  and  faster  than 
the  weaker  muscle  would  rotate  its  eye,  and  diplopia  would 
result,  except  for  nature's  wonderful  provision  for  prevent- 
ing it.  This  provision  is  the  basal  center,  presided  over  by 
the  fusion  faculty  of  the  mind,  which  stands  ever  ready  to 
send  a  supplemental  charge  of  neuricity  to  the  weaker  mus- 
cle in  order  than  there  may  be  harmonious  rotation  of  the 
two  eyes.     In  uncorrected  heterotropia,  binocular  single  vi- 


MUSCLES   EFFECTING   THEM.  31 

sion  is  impossible,  but,  notwithstanding  this,  the  volitional 
verting  centers  cause  the  eyes  to  rotate  as  if  they  were 
seeing  together ;  and  the  same  is  true  when  one  eye  is  blind. 
The  verting  centers  do  the  same  kind  of  work  whether  the 
eyes  are  orthophoric,  heterophoric  or  heterotropic,  and  even 
when  one  of  the  two  eyes  is  blind  from  disease.  Thus  it 
must  be  true  that  the  volitional  centers  that  control  the  vert- 
ing function  of  the  muscles  have  nothing  to  do  in  the  work 
of  correcting  heterophoric  conditions.  Nor  do  these  centers 
bear  any  causal  relationship  to  heterophoria  in  any  of  its 
forms.  These  centers  are  conjugate  because  they  join  in 
action  two  muscles,  one  belonging  to  each  eye;  they  are  vo- 
litional centers,  for  no  one  looks  either  to  the  right,  the  left, 
up,  down  or  in  any  oblique  direction,  without  first  will- 
ing to  do  so.  These  centers  are  all  in  the  motor  area  of  the 
cortex,  and  may  be  named,  arbitrarily,  the  first,  second, 
fourth,  fifth,  sixth,  seventh,  eighth  and  ninth  conjugate 
centers.  These  centers,  with  the  exception  of  the  second 
and  sixth,  are  excited  into  activity  for  only  a  short  period 
at  a  time,  the  gaze  rarely  being  prolonged  in  any  oblique 
direction  or  in  any  cardinal  direction,  except  down.  Pro- 
longed downward  look  is  common ;  and  during  this  time  the 
second  and  sixth  centers  are  in  continuous  action,  usually  in 
association  with  activity  of  the  third  conjugate  center,  or 
center  of  convergence,  which  is  also  a  volitional  center. 
Civilization  has  added  but  little,  if  any,  to  the  work  of  the 


32  OCULAR   ROTATIONS   AND   THE 

first,  fourth,  fifth  and  seventh  volitional  centers,  but  it  has 
created  immense  demands  on  the  second,  third,  sixth  and 
tenth  volitional  centers.  These  latter  centers  must  be  con- 
tinually discharging  neuricity  to  the  inferior  and  internal 
recti,  the  superior  obliques  and  the  ciliary  muscles,  respect- 
ively, throughout  the  continuance  of  near  work;  nor  can 
any  pose  of  the  head  bring  the  slightest  relief  to  the  third 
and  tenth  centers.  Dropping  the  head  forward,  its  usual 
pose  in  reading,  relieves  to  a  greater  or  less  extent  the  sec- 
ond and  sixth  centers,  the  relief  being  complete  when  the 
horizontal  plane  of  the  head  has  been  so  depressed  as  to  be 
at  right  angles  with  the  printed  page.  Reading  in  the  re- 
cumbent posture  adds  nothing  to  the  work  of  the  third  and 
tenth  centers,  but  it  adds  immensely  to  the  work  of  the  sec- 
ond and  sixth  centers.  The  third  and  tenth  centers  have 
rest  only  when  near  work  has  been  interrupted  by  closing 
the  eyes,  or  by  looking  into  infinity.  From  what  has  just 
been  said  it  would  appear  that  reading  or  other  near  work 
should  never  be  done  by  one  in  the  recumbent  posture ;  that, 
when  the  body  is  erect,  the  head  should  be  inclined  forward 
so  that  its  horizontal  plane  extended  might  point  towards,  if 
not  to,  the  printed  page  or  other  object  of  near  vision, 
for  the  relief  of  the  inferior  recti  and  superior  obliques  and 
the  second  and  sixth  centers  that  innervate  them ;  that  fre- 
quent, even  if  short,  intervals  of  rest  should  be  given  the 
internal  recti  and  the  ciliary  muscles  and  the  third  and 


MUSCLES   EFFECTING   THEM.  33 

tenth  centers  that  control  them,  by  closing  the  eyes  or  by 
changing  the  point  of  vision  to  some  distant  object  in  or 
above  the  horizon.  If  these  rules  are  not  observed,  near 
work  cannot  be  done  so  comfortably  nor  so  efficiently. 

Convergence. 

Convergence  pertains  only  to  the  internal  recti,  but  it  is 
normally  associated  with  accommodation.  Its  center,  the 
third  conjugate,  is  situated  in  the  cortex  and  is  under  the 
control  of  the  will.  No  better  name  could  be  given  this 
power  than  convergence.  The  angle  of  convergence  is  that 
formed  by  the  intersection  of  the  two  visual  axes,  and  at 
one  metre  is  twice  the  so-called  metre-angle  of  Nagel.  The 
distance  (base  line)  between  the  centers  of  the  two  eyes 
being  two  inches,  the  true  metre-angle  (the  angle  of  con- 
vergence at  one  metre)  is  2°  54'  38".  For  every  increase  of 
the  base  line  by  one-eighth  inch  the  metre  angle  is  increased 
10'  55".  The  angle  of  convergence  at  two  metres  is  one-half 
a  metre  angle,  and  convergence  at  one-half  a  metre  is  two 
metre  angles.  But  it  is  not  so  important  to  know  the  angle 
of  convergence  as  it  is  to  study  the  ease  with  which  it  may 
be  accomplished.  The  third  cortical  center  is  the  one  con- 
trolling convergence.  This  center  is  so  intimately  asso- 
ciated with  the  tenth  cortical  center,  the  one  controlling  the 
ciliary  muscles,  that  they  may  be  said  to  act  as  if  the  two 
constituted  one  center.    Normal  ciliary  muscles  and  perfect 


34  OCULAR   ROTATIONS   AND   THE 

balance  of  the  externi  and  interni  can  mean  nothing  else 
than  harmonious  accommodation  and  convergence. 

Weak  ciliary  muscles  and  normal  lateral  recti  muscles 
mean  inharmonious  accommodation  and  convergence.  Nor- 
mal ciliary  muscles  and  weak  interni  mean  want  of  har- 
mony between  accommodation  and  convergence.  Necessity 
for  ciliary  activity  for  distant  seeing,  as  in  hyperopia,  causes 
a  corresponding  contraction  of  the  interni,  which  would 
cause  convergence  except  for  activity  of  the  basal  centers 
governing  the  externi.  In  general  terms  it  may  be  stated : 
for  every  accommodative  diopter  of  neuricity  discharged  by 
the  tenth  cortical  center,  a  corresponding  convergence  diop- 
ter of  neuricity  is  discharged  by  the  third  cortical  center. 
The  normal  discharge  of  neuricity  by  the  tenth  center  for 
effecting  3  D  of  accommodation  in  emmetropic  eyes,  may  be 
stated  to  be  three  diopters,  and  the  same  quantity  discharged 
by  the  third  center  should  produce  the  necessary  converg- 
ence (three  metre  angles).  If  more  is  needed  because  of 
want  of  tonicity  of  the  interni,  supplemental  neuricity  is 
sent  from  the  right  and  left  third  basal  centers ;  if,  because 
of  too  great  tonicity  of  the  interni,  the  three  diopters  of 
neuricity  from  the  third  cortical  center  would  cause  too 
much  convergence,  this  effect  would  be  counteracted  by  a 
discharge  of  neuricity  from  the  right  and  left  fourth  basal 
centers  to  the  externi.  If  the  ciliary  muscles,  because  of 
inherent  weakness,  should  need  six  diopters  of  neuricity  for 


MUSCLES    EFFECTING    THEM.  35 

effecting  3  D  of  accommodation,  the  third  cortical  center 
would  also  discharge  six  diopters  of  neuricity  to  the  interni 
and  these,  having  normal  tonicity,  would  be  excited  into 
over-action.  Excessive  convergence  would  be  prevented 
only  by  excitation  of  the  right  and  left  fourth  basal  centers 
calling  into  corrective  action  the  two  externi. 

Carrying  a  test  object  towards  the  two  eyes,  to  determine 
how  near  it  may  be  made  to  approach  them  without  relaxa- 
tion of  convergence,  is  of  no  practical  value;  though  it  is 
well  known  that  some  eyes  can  attain  a  greater  angle  of 
convergence  than  others.  It  is  also  known  that,  as  a  rule, 
the  greater  the  accommodative  power  the  larger  the  possible 
angle  of  convergence;  and  yet  it  is  well  known  that  pres- 
byopia has  but  little  influence  over  convergence.  Failure 
of  ciliary  power,  because  of  age,  and  convergence  still  ac- 
tive; dissociation  of  accommodation  and  convergence,  in 
the  young,  by  convex  lenses  or  by  prisms;  and  myopia  and 
convergence,  these  would  all  seem  to  argue  against  the  idea 
that  the  third  and  tenth  conjugate  centers  act  as  if  only 
one  center.  It  may  be  that,  in  presbyopia,  the  tenth  center 
continues  to  send  neuricity  to  the  ciliary  muscles,  although 
they  may  be  no  longer  able  to  respond,  while  the  neuricity 
from  the  third  center  gets  ready  response  from  the  interni. 
Over-convergence,  when  the  eyes  are  going  under  the  influ- 
ence of  a  mydriatic,  can  be  explained  in  no  other  way  than 
that  the  maddened  tenth  center  generates  and  discharges  an 


36  OCULAR   ROTATIONS   AND   THE 

excess  of  neuricity  to  the  muscles  whose  power  is  waning, 
and  that  a  corresponding  excess  of  neuricity  is  sent  to  the 
interni.  There  seems  to  be  but  little  room  for  doubting 
that,  in  the  young  at  least,  the  third  and  tenth  conjugate 
centers  are  most  intimately  associated  in  action. 

The  convergence  test  should  be  made  with  the  monocular 
phorometer  at  the  reading  distance,  and  the  dot,  or  other 
test  object,  should  be  held  in  the  line  of  intersection  of  the 
extended  median  and  horizontal  planes  of  the  head.  The 
free  eye  should  be  the  one  used  in  fixation,  and  with  this 
eye  the  patient  should  look  sharply  at  the  true  object.  The 
displaced  image  in  the  other  eye  makes  fusion  impossible, 
nevertheless  there  will  be  convergence,  the  angle  depending 
on  these  two  conditions,  viz.:  first,  tonicity  of  the  ciliary 
muscles  and  of  the  interni ;  second,  the  quantity  of  neuricity 
discharged  by  the  third  and  tenth  cortical  centers.  The 
false  image  having  been  thrown  entirely  outside  the  retinal 
fusion  area,  the  fusion  faculty  cannot  excite  any  of  the  basal 
centers.  If,  in  the  distant  test,  lateral  orthophoria  has  been 
shown,  the  false  object  should  be  directly  under  the  true 
in  the  near  test.  If  the  convergence  is  too  great  (pseudo- 
esophoria) ,  it  shows  that  the  tonicity  of  the  ciliary  muscles 
is  too  low,  and  that  they  demand  an  excessive  amount  of 
neuricity  from  the  tenth  conjugate  center  for  effecting  the 
necessary  accommodation.  This  over-excitation  of  the  tenth 
center  causes  a  corresponding  over-excitation  of  the  third 


MUSCLES   EFFECTING   THEM.  37 

conjugate  center,  hence  over-action  of  the  interni  (pseudo- 
esophoria).  Or  if  the  tonicity  of  the  interni  is  too  high 
(sthenic  orthophoria),  the  normal  quantity  of  neuricity 
from  the  third  cortical  center  excites  too  much  contractility. 
In  either  case  the  pseudo-esophoria  would  be  shown.  Such 
eyes,  when  engaged  in  near  work,  are  prevented  from  cross- 
ing by  excitation  of  the  right  and  left  fourth  basal  centers, 
which  call  into  corrective  or  fusional  activity  the  two  ex- 
terni. 

When  the  near  test  shows  want  of  convergence,  or  pseudo- 
exophoria,  the  distant  test  having  revealed  orthophoria,  one 
of  two  conditions  exists :  first,  the  ciliary  muscles  have  high 
tonicity  and  demand  less  neuricity  than  normal  for  effecting 
accommodation,  hence  the  third  conjugate  center  fails  to 
furnish  enough  neuricity  to  effect  the  required  convergence; 
or,  second,  the  tonicity  of  the  interni  is  low  (asthenic  ortho- 
phoria), and  the  normal  impulse  sent  from  the  third  conju- 
gate center  fails  to  make  them  converge  the  visual  axes  suf- 
ficiently. In  either  case  the  near  use  of  such  eyes  makes 
it  necessary  for  the  fusion  faculty  to  bring  into  action  the 
right  and  left  third  basal  centers,  that  enough  convergence 
may  be  had.  Unlike  the  volitional  centers  that  control  ver- 
sion of  the  eyes,  the  convergence  center,  as  already  shown, 
may  cause  one  form  of  heterophoria,  viz.,  pseudo-hetero- 
phoria,  which  may  be  either  pseudo-esophoria  or  pseudo- 
exophoria.     The  former  may  be  shown  in  both  the  far  and 


38  OCULAR   ROTATIONS   AND    THE 

near  phorometric  tests,  but  the  latter  can  be  shown  only  in 
the  near  test. 

The  third  cortical  center,  or  center  of  convergence,  is 
sometimes  absent,  as  is  shown  by  inability  to  converge,  al- 
though right  and  left  versions  are  normal. 

DUCTION. 

Of  the  three  kinds  of  power  of  the  ocular  muscles,  the 
duction  power  is  the  most  important,  when  there  are  two 
eyes,  for  this  power  exists  only  in  the  interest  of  binocular 
single  vision.  While  the  centers  that  effect  version  and  con- 
vergence are  situated  in  the  cortex  and  each  one  is  connected 
with  two  muscles,  one  belonging  to  each  eye,  and  these  cen- 
ters are  under  the  control  of  the  will,  the  duction  centers 
are  basal,  and  each  is  connected  with  only  one  muscle,  and 
they  are  controlled  by  the  fusion  faculty  of  the  mind.  These 
centers  always  stand  ready  to  send  supplemental  neuricity 
to  either  muscle  of  a  pair  wanting  in  tonicity.  They  also 
stand  ready  to  lead  the  eye  into  a  proper  position  for  placing 
the  macula  under  a  displaced  image ;  or,  if  both  images  have 
been  displaced,  the  duction  power  will  be  excited  so  as  to 
place  the  macula  of  each  eye  under  its  proper  image.  There 
is,  in  each  eye,  a  field  on  any  part  of  which  other  than  the 
macula  one  of  the  two  images  of  an  object  may  fall,  the 
other  image  being  on  the  macula,  and  yet  produce  only  tem- 
porary diplopia ;  for  the  fusion  faculty,  having  the  mastery 


MUSCLES   EFFECTING    THEM. 


39 


of  this  field,  as  well  as  of  the  basal  centers,  calls  into  activity 
one  or  more  of  the  basal  centers  for  leading  the  eye  into  a 
position  that  will  place  its  macula  under  the  image. 

The  fusion  field  of  the  retina  can  be  mapped  out  with  a 
high  degree  of  accuracy,  and  this  field  always  includes  the 
macula.  Measuring  from  the  macula  along  the  horizontal 
meridian,  the  nasal  extent  of  this  field  is  about  8°  of  prism, 


Fig.  5. 


and  the  temporal  extent  of  the  field  is  25°  to  35°  of  prism; 
but  above  and  below  the  macula,  along  the  vertical  me- 
ridian, this  field  measures  only  about  3°  of  prism.  Con- 
necting each  of  the  two  points  on  the  horizontal  meridian, 
marking  the  nasal  and  temporal  limits  of  the  fusion  field, 
with  the  two  points  on  the  vertical  meridian,  marking  the 
upper  and  lower  limits  of  this  field,  an  area  will  be  included 
somewhat  kite-shaped,  the  tail  of  the  kite  being  towards  the 


40  OCULAR   ROTATIONS   AND   THE 

temple,  while  the  head  of  the  kite  is  towards  the  nose.  This 
area  is  the  retinal  fusion  field.  The  two  images  of  an  ob- 
ject of  fixation  can  be  fused  only  when  they  fall  on  the  macu- 
las.  If  one  of  the  images  is  on  the  macula,  and  the 
other  image  on  some  other  part  of  the  fusion  area,  the  object 
is  doubled  until  the  eye,  seeing  the  false  object,  is  led  into 
such  a  position  as  will  place  its  macula  under  the  misplaced 
image.  This  accomplished,  the  two  eyes  see  only  one  object, 
but  only  one  eye  is  pointing  towards  it.  If  the  misplaced 
image  is  thrown  on  a  part  of  the  retina  entirely  outside  the 
fusion  area,  no  attempt  is  made  to  fuse  the  two  images,  and 
the  object  remains  double,  but  both  eyes  point  towards  the 
true  object. 

Even  in  orthophoria  a  study  of  the  duction  power  of  the 
muscles  is  important,  for  while  the  two  muscles  of  a  pair 
may  be  equal  in  tonicity,  both  may  be  wanting  in  contractile 
power.  This  want  can  be  detected  more  easily  by  the  duc- 
tion test  than  by  the  version  test. 

In  heterophoria  the  muscle  that  is  stronger  than  its  an- 
tagonist may  not  possess  in  itself  too  much  contractile 
power,  and  this  is  better  shown  by  the  duction  test  than  by 
the  version  test.  In  no  case  of  heterophoria  can  the  proper 
treatment  be  resorted  to  without  a  knowledge  of  the  duction 
power  of  the  muscles  concerned.  In  a  case  of  exophoria, 
the  externus  should  not  be  weakened  by  a  partial  tenotomy 
unless  its  duction  power  has  been  shown  to  be  more  than 


MUSCLES   EFFECTING   THEM.  41 

8° ;  unless  abduction  has  been  ascertained  to  be  less  than 
6°  or  8°,  a  shortening  or  advancement  of  an  internus  should 
not  be  done  for  an  exophoria. 

Normal  abduction,  or  the  power  that  an  externus  has  to 
lead  its  eye  so  that  the  macula  may  be  brought  under  an 
image  that  has  been  displaced  toward  the  nose,  in  the  field 
of  fusion,  is  6°  to  8°.  The  neuricity  that  causes  this  con- 
tractility comes  from  the  fourth  basal  center  on  the  corre- 
sponding side. 

Normal  adduction,  or  the  power  that  ?n  internus  has  to 
lead  its  eye  into  a  position  that  will  place  the  macula  under 
an  image  that  has  been  thrown  towards  the  temple,  in  the 
fusion  area,  is  25°  to  35°.  This  power  comes  from  the  third 
basal  center  on  the  corresponding  side. 

Normal  superduction,  or  the  power  that  a  superior  rectus 
has  to  so  lead  its  eye  that  the  macula  may  be  brought  under 
an  image  that  has  been  displaced  downward,  in  the  fusion 
field,  is  2°  to  3°.  The  impulse  causing  the  contractility 
comes  from  the  first  basal  center  on  the  same  side. 

Normal  subduction,  or  the  contractile  power  that  an  in- 
ferior rectus  has  for  leading  its  eye  into  a  position  that  will 
place  its  macula  under  an  image  that  has  been  displaced 
upward,  in  the  fusion  field,  is  2°  to  3°.  This  movement  is 
effected  by  the  neuricity  from  the  second  basal  center  on  the 
corresponding  side. 

The    above    duction    measurements    presuppose    normal 


42  OCULAR   ROTATIONS   AND   THE 

tonicity  of  the  muscle  measured,  and  that  its  basal  center  is 
likewise  normal  in  that  it  is  under  the  perfect  control  of  the 
fusion  faculty  of  the  mind.  The  cause  of  any  variation 
from  these  measurements  resides  either  in  the  muscle  or 
in  the  basal  center  that  controls  it.  If  there  is  an  excess  of 
duction  power  and  the  cause  is  in  the  muscle  itself,  there  is 
too  much  tonicity  due  to  excess  in  size,  or  to  the  fact  that 
its  attachment  to  the  globe  is  in  front  of  the  usual  line  of 
attachment ;  if  the  cause  of  the  excess  is  in  the  basal  center 
that  excites  the  contractility,  the  only  explanation  is  that 
the  center  is  capable  of  storing  and  discharging  an  abnor- 
mally large  quantity  of  .neuricity.  If  the  duction  power  is 
less  than  normal  and  the  cause  resides  in  the  muscle,  it  is 
because  the  muscle  is  too  small  or  that  its  attachment  to  the 
globe  is  behind  the  normal  line  of  attachment;  but  if  the 
cause  is  in  the  basal  center,  the  explanation  would  seem  to 
be  that  the  center  is  incapable  of  storing  and  discharging 
the  proper  quantity  of  neuricity. 

As  has  been  shown  already,  the  basal  centers  are  per- 
fectly at  rest  in  every  correct  test  for  heterophoria,  for  the 
reason  that,  in  making  such  a  test,  the  false  image  has  been 
thrown  entirely  beyond  the  limits  of  the  field  of  fusion. 
The  fusion  faculty  of  the  mind,  under  such  a  condition,  is 
wholly  unable  to  excite  into  activity  a  single  basal  center. 
The  basal  centers  never  enter  into  the  causation  of  hetero- 
phoria, but  stand  ready  always  to  respond  to  the  demands 


MUSCLES   EFFECTING   THEM.  43 

of  the  fusion  faculty  of  the  mind,  for  correcting  heterophoric 
conditions. 

Prism  test  for  duction. — This  test  should  be  applied  to 
only  one  eye  at  a  time.  The  head  should  be  erect  and  the 
test  object  should  be  at  20  feet  or  more  distant,  and  prac- 
tically in  the  line  of  intersection  of  the  extended  median 
and  horizontal  fixed  planes  of  the  head.  The  object  should 
be  either  a  small  light  or  a  white  dot  on  a  blackboard.  One 
of  two  methods  of  using  the  prisms  may  be  adopted.  The 
first,  but  not  the  best,  is  to  place  a  weak  prism  before  the 
eye  and  then  successively  place  stronger  prisms  until  the 
muscle  under  test  can  no  longer  fuse  the  image  in  its  eye 
with  the  image  in  the  other  eye,  the  test  object  now  being 
seen  as  two  objects.  It  must  be  remembered  that  the  apex 
of  the  prism  points  towards  the  muscle  whose  duction  power 
is  being  taken,  and  that  the  image  is  displaced  towards  the 
base  of  the  prism. 

Abduction. — In  testing  abduction  the  base  of  the  prism 
must  be  towards  the  nose  while  the  apex  points  towards  the 
temple.  The  axis  of  the  prism  must  lie  in  the  horizontal 
plane  of  the  head.  Placing  a  1°  prism  thus,  the  externus 
immediately  moves  the  macula  under  the  displaced  image 
and  vision  becomes  single.  The  same  thing  is  true,  but 
not  quite  so  rapidly,  when  2°,  3°,  4°,  5°,  6°,  7°  and 
8°  prisms  are  so  placed,  the  externus  being  possessed  of 
normal  duction  power.     If  the  tonicity  test  has  shown  lat- 


44  OCULAR   ROTATIONS   AND   THE 

eral  orthophoria,  and  abduction  is  8°  or  more,  the  con- 
dition is  sthenic  orthophoria;  but  the  condition  is  asthenic 
orthophoria  if  abduction  is  much  less  than  6°  or  8°.  If  the 
tonicity  test  reveals  exophoria,  an  abduction  of  more  than 
8°  shows  that  the  externus  is  intrinsically  too  strong,  but 
an  abduction  of  less  than  8°  shows  that  the  externus  is  not 
intrinsically  too  strong.  If  the  tonicity  test  reveals  esopho- 
ria,  an  abduction  of  8°,  a  little  less  or  a  little  more,  shows 
that  the  inherent  power  of  the  internus  is  too  great,  but  if 
the  abduction  is  much  less  than  8°,  the  indication  is  that 
the  internus  is  not  too  strong  intrinsically.  The  abduction 
test  is  valuable  for  the  reason  that  it  gives  reliable  informa- 
tion as  to  what  muscle  should  be  operated  on  in  either  exo- 
phoria or  esophoria.  It  answers  the  question  better  than 
anything  else  can:  "Should  the  too  strong  muscle  be  made 
weaker  by  a  partial  tenotomy,  or  should  the  weaker  muscle 
be  made  stronger  by  a  shortening  or  advancement?" 

The  faculty  of  the  mind  that  presides  over  all  duction  cen- 
ters is  the  fusion  faculty,  and  the  center  by  means  of  which 
abduction  is  controlled  is  the  fourth  basal  center.  This 
center  seems  incapable  of  over-excitation,  hence  abduction 
can  be  increased  only  as  muscle  tone  is  increased  by  either 
exercise  or  by  operation. 

Adduction. — The  test  for  adduction  cannot  be  relied  upon, 
for  the  reason  that  the  third  basal  center  which  controls  it 
is  a  very  excitable  and  powerful  center.     This  is  shown  by 


MUSCLES   EFFECTING   THEM.  45 

the  fact  that  adduction  can  be  greatly  increased  although 
there  has  not  been  time  nor  effort  for  improving  the  tonicity 
of  the  internus.  Normal  adduction  is  stated  by  most  au- 
thors to  be  about  three  times  greater  than  abduction;  but 
it  is  well  known  that  adduction  in  some  cases  may  be  made 
to  reach  50°  or  more,  after  a  few  trials.  In  some  cases, 
however,  adduction  is  very  low,  and  repeated  efforts  fail  to 
increase  it  much.  In  making  the  test  for  adduction,  by 
prisms  from  the  trial  case,  the  base  of  each  prism  is  toward 
the  temple  and  expex  points  towards  the  nose,  the  axis  of 
the  prism  lying  in  the  horizontal  plane  of  the  head.  Be- 
ginning with  a  5°  prism,  the  strength  is  increased  by  5° 
with  every  change,  until  the  internus  no  longer  receives  a 
fusion  impulse,  the  false  image  having  been  thrown  temple- 
ward  entirely  outside  the  retinal  fusion  area. 

Subduction. — To  test  the  duction  power  of  the  inferior 
rectus,  by  prisms  from  the  trial  case,  a  V20  prism  is  placed 
apex  down  and  is  so  held  that  its  axis  is  parallel  with  the 
median  plane  of  the  head.  With  every  change  of  prisms 
there  should  be  an  increase  of  Vfc°>  until  that  prism  has 
been  placed  which  cannot  be  overcome  by  the  muscle,  for 
the  reason  that  it  receives  no  impulse  from  its  second  basal 
center,  the  false  image  having  been  thrown  entirely  beyond 
the  upper  boundary  of  the  retinal  area  over  which  the  fu- 
sion faculty  has  control.  The  strength  of  the  last  prism 
that  the  muscle  could  overcome  is  the  measure  of  its  duction 


46  OCULAR   ROTATIONS   AND   THE 

power.  This  is  placed,  by  most  authors,  at  3°,  but  it  is 
oftener  less  than  more. 

Superduction. — The  duction  power  of  the  superior  rectus 
is  taken  precisely  in  the  same  manner  as  set  forth  in  the 
paragraph  on  subduction,  with  the  exception  that  each 
prism  must  be  held  with  its  apex  up.  Under  the  stimulus 
of  its  basal  center  (the  first)  the  superior  rectus,  with  nor- 
mal tonicity,  should  overcome  a  prism  of  3°.  Rarely  is  its 
duction  power  more,  while  very  often  it  is  less  than  3°.  If 
the  eye  under  test  is  hyperphoric  superduction  may  be  con- 
siderably more  than  3°.  Whatever  may  be  the  quantity  of 
hyperphoria,  the  superior  rectus  that  cannot  overcome  a 
prism  of  more  than  3°  should  not  be  weakened  by  a  partial 
tenotomy.  An  operation  on  a  superior  rectus  should  never 
reduce  its  duction  power  below  3°. 

In  taking  the  duction  power  of  any  muscle  by  means  of 
the  prisms  in  the  trial  case,  only  one  eye  should  be  tested 
at  a  time.  The  image  in  the  eye  not  under  test  should  be 
constantly  on  the  macula,  and  both  the  head  and  the  eye 
should  be  in  their  primary  positions.  So  long  as  the  image 
in  this  eye  remains  unmoved,  no  neuricity  will  be  sent  to 
any  one  of  its  six  muscles,  from  either  their  cortical  or  basal 
centers.  When  the  prism  is  held  before  the  eye  whose  mus- 
cle is  to  be  tested,  the  image  of  the  test  object  is  thrown 
from  the  macula  in  the  direction  of  the  base  of  the  prism. 
If  it  falls  within  the  fusion  area  toward  the  nose,  the  fusion 


MUSCLES    EFFECTING   THEM.  47 

faculty  of  the  mind  instantly  discharges  from  the  fourth 
basal  center  a  quantity  of  neuricity  that  will  make  the  ex- 
ternus  move  the  eye,  at  once  and  quickly,  so  as  to  bring  the 
macula  under  the  displaced  image.  If  the  image  falls  be- 
yond the  nasal  border  of  the  fusion  field,  no  neuricity  is  sent 
from  the  fourth  basal  center  to  the  externus  and  the  eye  re- 
mains still,  provided  there  is  no  lateral  heterophoria.  If 
there  is  a  lateral  heterophoria  the  eye,  no  longer  influenced 
by  the  fusion  faculty,  assumes  its  position  of  rest,  or  that 
position  into  which  the  tonicity  of  all  the  muscles  would 
place  it. 

If  the  displaced  image  falls  on  the  fusion  area,  the  direc- 
tion in  which  it  has  been  thrown  determines  which  basal 
center  shall  be  discharged  by  the  touch  of  the  fusion  faculty, 
and  which  muscle  shall  be  made  to  lead  the  macula  under 
the  false  image :  nasal-ward,  the  fourth  basal  center  and  the 
externus ;  temple- ward,  the  third  basal  center  and  the  inter- 
nus;  below,  the  first  basal  center  and  the  superior  rectus; 
above,  the  second  basal  center  and  the  inferior  rectus.  In 
either  case  the  discharge  is  sudden,  full  and  sufficiently  pow- 
erful to  effect  a  quick  rotation,  that  there  may  be  no  pro- 
longed diplopia. 

Rotary  Prism. — The  easiest  and  best  means  for  deter- 
mining the  duction  power  of  any  rectus  muscles  is  the  rotary 
prism  of  the  monocular  phorometer.  With  this  instrument 
the  image  is  not  thrown,  but  is  made  to  glide,  in  a  definite 


48  OCULAR   ROTATIONS   AND   THE 

direction,  but  at  no  time  is  the  image  allowed  to  leave  the 
macula,  until  the  duction  power  of  the  muscle  has  been  sur- 
passed. Diplopia  does  not  occur  so  long  as  the  macula  is 
kept  under  the  moving  image.  The  moment  the  fusion 
faculty  allows  the  basal  center  involved  to  cease  discharging 
neuricity  to  the  muscle  whose  gradually  increasing  contrac- 
tion has  kept  the  macula  under  the  moving  image,  that  mo- 
ment diplopia  occurs,  the  false  object  moving  rapidly  from 
the  true.  The  fusion  task  having  been  abandoned,  the  eye 
assumes  the  position  of  tonicity  of  all  its  muscles;  and  the 
image  rests  beyond  the  border  of  the  fusion  area  until  the 
prism  is  rotated  backward  towards  the  neutral  position. 
Only  10°  of  duction  can  be  measured  by  the  unaided  rotary 
prism,  but  this  is  more  than  sufficient  for  determining 
sub-  and  superduction  and  abduction,  when  there  is  ortho- 
phoria. In  taking  adduction  the  15°  supplementary  prism 
must  be  placed  base  out  behind  the  rotary  prism,  10°  of  the 
power  being  neutralized  by  placing  the  index  of  the  rotary 
prism  at  the  10°  abduction  mark.  Thus,  beginning  with 
5°  displacement  of  the  image  temple-ward,  which  is  easily 
overcome  by  the  internus,  the  rotary  prism  is  revolved  back 
through  the  abduction  arc  into  the  adduction  arc.  After 
passing  the  zero  mark,  every  degree  of  rotation  adds  to  the 
full  effect  of  the  15°  prism,  and  when  the  full  adduction  arc 
has  been  traversed  by  the  index  of  the  rotary  prism,  the 
combined  effect  is  25°.     If  diplopia  has  not  yet  occurred 


MUSCLES   EFFECTING   THEM.  49 

adduction  is  more  than  25° ;  if  it  occurs  while  the  rotary 
prism  is  on  its  way  to  the  10°  adduction  mark,  the  position 
of  the  index  is  noted,  and  if  it  stands  at  8°,  at  the  moment 
of  diplopia,  adduction  is  23°  (15°~8°).  To  find  higher  ad- 
duction than  25°,  the  10°  supplemental  prism  must  be 
placed  base  out,  in  front  of  the  rotary  prism,  while  the  15° 
prism  remains  in  the  cell  behind  it.  The  two  sup- 
plemental prisms  have  a  combined  displacing  power  of  25°, 
but  10°  of  this  power  should  be  neutralized,  at  the  begin- 
ning, by  placing  the  index  of  the  rotary  prism  at  10°  in  the 
abduction  arc.  The  remaining  15°  is  easily  overcome  by 
a  very  strong  interims.  When  the  rotary  prism  has  been 
revolved  until  its  index  stands  at  zero,  the  adduction,  up 
to  this  point,  is  25° ;  as  the  index  moves  in  the  adduction 
arc,  every  degree  of  advance  adds  that  much  to  the  25°  of 
the  two  supplementary  prisms.  If  diplopia  occurs  when 
the  index  points  to  8°,  the  adduction  is  33°  (25°+8°). 
Higher  adduction  than  35°  cannot  be  taken  easily  with  the 
monocular  phorometer.  Ordinarily  a  normal  discharge  of 
neuricity  from  the  third  basal  center  to  an  internus,  even 
when  there  is  esophoria,  does  not  produce  more  than  35° 
adduction. 

When  abduction  is  more  than  10°,  which  is  often  the  case 
in  exophoria,  the  rotary  prism  must  be  aided  by  the  10° 
supplementary  prism.  This  should  be  placed  base  towards 
the  nose,  in  the  cell  behind  the  rotary  prism,  and  its  power, 


50  OCULAR   ROTATIONS   AND    THE 

at  first,  should  be  neutralized  by  placing  the  index  of  the 
rotary  prism  at  10°  in  the  adduction  arc.  Moving  the  index 
to  zero,  the  full  power  of  the  supplemental  prism  is  made 
manifest ;  carrying  the  index  into  the  abduction  arc,  the  dis- 
placemnt  of  the  image  nasal-ward  is  increased,  and  the 
externus  must  contract  still  more,  to  keep  the  macula  under 
the  moving  image.  The  moment  diplopia  occurs  the  rotary 
prism  must  be  stopped.  If  now  the  index  stands  at  5°, 
the  abduction  is  15°  (10°+5°)  ;  if  the  index  stands  at 
10°,  abduction  is  20°  (10V10°).  Cases  of  exophoria  are 
rare  in  which  abduction  is  greater  than  20°,  but  when  it  is, 
then  the  15°  supplemental  prism  should  replace  the  10° 
prism. 

The  value  of  the  duction  test  is  great,  whether  made  with 
prisms  from  the  test  case  or  by  means  of  the  rotary  prism. 
Its  value  is  greatly  lessened  if  the  head  is  not  in  the  primary 
position,  and  if  one  eye  is  not  allowed  to  remain  in  the  pri- 
mary position  throughout  every  test.  The  sole  object  of  the 
test  is  to  determine  the  influence  that  the  fusion  faculty  of 
the  mind  has  over  one  basal  center  to  excite  the  contractile 
power  of  one  muscle,  in  the  interest  of  binocular  single 
vision.  To  accomplish  this  there  must  be  no  displacing 
prism  before  one  eye;  and  the  axis  of  the  displacing  prism 
before  the  other  eye  must  point  in  one  of  the  four  cardinal 
directions. 

The  author  recognizes  the  fact  that,  in  sub-  and  super- 


MUSCLES   EFFECTING   THEM.  51 

duction,  two  centers  are  excited,  one  of  these  controlling  a 
rectus  muscle  and  the  other  an  oblique  muscle ;  but  for  prac- 
tical purposes  this  double  excitation  should  be  ignored,  only 
the  rectus  muscle  and  its  center  being  kept  in  mind. 

Whenever  the  axis  of  the  displacing,  or  duction,  prism  is 
held  obliquely,  two  recti  muscles  and  their  centers  are  ex- 
cited into  activity. 

Low  duction  in  orthophoria  indicates  ceiling-to-floor  and 
wall-to-wall  exercise ;  high  duction  power  in  orthophoria  in- 
dicates that  there  is  nothing  to  -be  done  to  the  recti.  Low 
abduction  in  exophoria  contra-indicates  a  partial  tenotomy 
of  the  externus,  and  indicates  a  shortening  of  the  internus ; 
high  abduction  in  exophoria  indicates  a  partial  tenotomy  of 
the  externus  and  contra-indicates  a  shortening  of  the  in- 
ternus. In  esophoria  adduction  cannot  be  depended  on  so 
certainly  as  can  abduction,  in  the  effort  to  determine  on 
what  muscle  an  operation  should  be  done  and  the  character 
of  the  operation.  Very  low  abduction  in  esophoria  would 
indicate  a  shortening  of  the  externus ;  abduction  approxi- 
mating 8°  would  indicate  a  partial  tenotomy  of  the  internus. 
The  version  test  can  be  relied  on  in  determining  the  muscle 
to  be  operated  upon,  but  not  so  implicitly  as  can  the  duction 
test.  Only  the  tonicity  test  of  the  obliques  can  determine 
whether  a  tenotomy  of  a  rectus  muscle  should  be  central  or 
marginal,  and  whether  a  shortening  or  advancement  should 
be  so  done  as  to  change  the  rotation  plane  of  the  muscle. 


52  OCULAR   ROTATIONS   AND   THE 

Why  muscles  with  equal  tonicity  should  not  have  equal 
duction  power  seems  susceptible  of  only  one  explanation, 
viz. :  the  muscle  that  has  the  greater  duction  power,  as  the 
internus,  has  the  more  powerful  basal  center ;  and  the  mus- 
cle that  has  the  weaker  duction  power,  as  the  externus,  has 
a  weaker  basal  center.  Difference  in  the  quantity  of  neu- 
ricity  sent  by  a  basal  center  to  a  muscle  determines  the  dif- 
ference in  duction  power,  in  orthophoric  cases.  This  is 
made  more  apparent  by  recalling  the  fact  that,  in  lateral 
orthophoria,  abversion  is  equal  to  adversion,  to  effect  which 
neuricity,  from  a  common  source,  is  sent  in  equal  quantities 
to  the  externus  of  one  eye  and  the  internus  of  the  other. 

Cyclo-duction. — The  duction  power  of  an  oblique  muscle 
(cyclo-duction)  can  be  taken  with  the  clinoscope.  The 
translucent  discs,  with  lines  entirely  across,  must  be  used, 
and  they  must  be  so  placed  that  both  lines  shall  be  either 
vertical  or  horizontal.  With  the  tubes  properly  adjusted 
the  two  lines  would  be  seen  as  one.  Revolving  one  tube 
would  displace  one  line,  which  would  cause  a  corresponding 
change  in  position  of  the  retinal  image  of  that  line.  To  pre- 
vent diplopia  the  fusion  faculty  of  the  mind  calls  into  ac- 
tion the  basal  center  that  controls  the  action  of  an  oblique, 
thus  torsioning  the  eye  so  that  the  image,  though  changed 
in  position,  shall  still  lie  on  the  original  meridian. 

It  is  well  known  that  there  is  a  greater  disposition  on  the 
part  of  the  mind  to  fuse  horizontal  lines  than  there  is  to  fuse 


MUSCLES   EFFECTING   THEM.  53 

vertical  lines.  The  only  explanation  for  this  is  that  the  fu- 
sional  retinal  area  is  many  times  longer  (horizontally)  than 
it  is  wide  (vertically),  so  that  the  image  of  the  horizontal 
line  would  lie  almost,  if  not  entirely,  in  the  fusional  area, 
while  a  good  part  of  the  image  of  a  vertical  line  would  fall 
on  retinal  surface  outside  the  fusional  area.  In  the  former 
case  the  fusion  stimulus  would  be  greater  than  in  the  latter. 
For  this  reason  the  test  lines  should  be  placed  horizontally 
in  the  clinoscope.  Thus  placed,  if  the  one  tube  is  revolved 
so  as  to  make  its  line  dip  toward  the  opposite  side,  the  su- 
perior oblique  of  the  corresponding  eye  is  excited  into  action 
by  its  proper  basal  center  (the  sixth),  under  the  guidance  of 
the  fusion  faculty  of  the  mind.  The  revolving  of  the  tube  is 
continued  until  the  lines  begin  to  double.  The  index  shows 
the  extent  of  the  revolution  of  the  tube,  and  the  degree  of 
the  torsion  accomplished  by  the  superior  oblique  (minus 
cyclo-duction) ,  in  the  effort  to  keep  the  image  in  its  eye 
fused  with  the  image  in  the  fellow  eye. 

To  test  the  fusion  power  of  the  inferior  oblique  (plus 
cyclo-duction) ,  one  tube  must  be  revolved  so  as  to  make  the 
line  dip  towards  the  corresponding  side.  Minus  cyclo- 
duction  and  plus  cyclo-duction  are  practically  equal,  and 
each,  with  the  clinoscope,  may  be  as  much  as  14°,  but  it  is 
more  often  less. 

The  cyclophorometer  is  easier  to  adjust  than  the  clino- 
scope, and  is  just  as  accurate  in  determining  cyclo-duction. 


54  OCULAR   ROTATIONS. 

It  is  made  on  the  principle  that  the  test  lines  (streaks  of 
light)  should  always  be  horizontal.  At  first  the  instrument 
should  be  arranged  as  in  testing  for  cyclophoria;  that  is, 
the  triple  rods  should  be  placed  in  their  cells  with  axes  verti- 
cal, each  index  pointing  to  zero.  A  displacing  prism  should 
be  placed,  base  up,  behind  one  triple  rod.  The  room  should 
be  darkened  and  the  test  object  should  be  a  candle  blaze, 
or,  better  still,  a  bright  point  of  light.  With  the  instrument 
properly  leveled,  two  horizontal  streaks  of  light  should  be 
seen,  and  their  ends  should  be  made  even  by  means  of  the 
adjustment  screw.  On  removing  the  displacing  prism  the 
two  streaks  are  at  once  fused.  To  test  the  fusion  power  of 
a  superior  oblique  (minus  cyclo-duction) ,  the  rod  before  the 
eye  under  the  test  should  be  revolved  in  the  lower  temporal 
arc  until  the  line  of  light  begins  to  double.  The  index  will 
show  the  degrees  of  displacement  of  the  image,  and  the 
amount  of  torsion  that  has  been  effected  to  prevent  diplopia. 

To  test  the  fusion  power  of  an  inferior  oblique  (plus  cyclo- 
duction),  the  triple  rod  before  the  eye  under  test  should  be 
revolved  in  the  lower  nasal  arc  until  the  line  of  light  begins 
to  double.  The  index  points  to  the  number  of  degrees  of 
torsion  that  has  been  effected  in  the  interest  of  fusion. 

The  instrument  for  testing  cyclo-duction  must  necessarily 
be  a  binocular  instrument ;  but  it  is  important  that  only  one 
muscle  of  one  eye  shall  be  under  test  at  one  and  the  same 
time. 


CHAPTER  II. 


THE  BRAIN   CENTERS   CONTROLLING 
THE    OCULAR    MUSCLES. 


The  following  study  of  the  action  of  the  ocular  muscles, 
from  the  brain  side  of  the  question,  is  based  on  pathology 
and  physiology,  and  not  on  anatomy  and  histology.  Ex- 
perimentation on  the  lower  animals  has  shown  that  irrita- 
tion at  a  certain  point  of  the  motor  area  of  the  left  cortex 
will  cause  both  eyes  to  turn  to  the  right,  spasmodically,  and 
that  destruction  of  this  part  of  the  cortex  will  cause  both 
eyes  to  turn  paralitically  in  the  other  direction.  Irrita- 
tive and  destructive  disease  of  the  cortex,  in  human  beings, 
have  shown  the  same  thing. 

There  seems  no  good  reason  for  doubting  the  existence 
of  conjugate  cortical  brain  centers  for  the  control  of  the 
ocular  muscles,  notwithstanding  the  fact  that  the  scalpel 
and  the  microscope  can  never  trace  the  two  fibers,  or  two 
sets  of  fibrils,  from  the  one  common  brain  center  to  the  two 
muscles  (one  belonging  to  each  eye)  under  its  control. 

Maddox,  in  his  admirable  work,  "The  Ocular  Muscles," 
says :  "The  number  of  conjugate  innervations  is,  at  present, 

(55) 


56  THE   BRAIN   CENTERS 

unknown.  Five  have  long  been  recognized;  of  which  one 
elevates  both  eyes,  another  depresses  them,  a  third  turns 
both  to  the  right,  and  a  fourth  both  to  the  left.  The  fifth 
is  the  convergence  innervation."  Continuing,  he  says :  "Be- 
sides these  five,  I  imagine  there  may  be  three  which  govern 
torsion,  and  two  which  regulate  the  vertical  balance  of  the 
eyes." 

In  his  former  work,  "Ophthalmic  Myology,"  the  author 
taught  that  there  are  nine  conjugate  innervation  centers  for 
the  control  of  the  twelve  extrinsic  ocular  muscles ;  that  five 
of  these  centers  are  connected  with  the  eight  recti  muscles, 
each  center  with  two  muscles,  one  of  which  belongs  to  the 
right  eye,  the  other  belonging  to  the  left  eye;  that  four  of 
the  nine  centers  are  connected  with  the  four  oblique  mus- 
cles, each  center  with  two  muscles,  one  belonging  to  the 
right  eye,  the  other  to  the  left  eye.  During  the  three  years 
that  have  intervened,  the  author  has  not  had  cause  for 
changing  his  mind  as  to  the  existence  of  these  nine  conju- 
gate brain  centers;  but  his  views  as  to  the  exact  character 
of  work  done  by  these  centers  have  been  changed  some- 
what, as  the  result  of  further  study.  More  than  two  years 
ago  the  author  recognized  the  fact  that  the  conjugate  brain 
centers  could  make  the  muscles  obey  the  law  of  binocular 
rotations,  only  when  the  muscles  of  each  pair  are  perfectly 
balanced — when  there  is  orthophoria.  The  explanation 
that  the  upward  rotation  could  be  accomplished  without  di- 


AND   THE   OCULAR    MUSCLES.  57 

plopia,  when  one  eye  is  hyperphoric  and  the  other  cata- 
phoric, by  an  unequal  discharge  of  neuricity  from  the  first 
conjugate  center  to  the  two  superior  recti,  the  greater  quan- 
tity going  to  the  weaker  muscle,  was  not  satisfactory.  It 
seems  more  reasonable  to  suppose  that  when  a  conjugate 
center  discharges  its  stored  neuricity,  it  is  equally  divided 
between  the  two  muscles.  To  make  the  weaker  muscle  ro- 
tate its  eye  in  perfect  harmony  with  the  eye  having  the 
stronger  muscle,  there  must  come  to  the  former,  from  some 
other  source,  a  supplemental  quantity  of  nerve-force. 
Whence  this  added  force  and  what  mind-power  controls  it? 
The  answer  was  first  given  at  the  meeting  of  the  Section 
of  Ophthalmology  of  the  American  Medical  Association,  in 
New  Orleans,  in  1903,  by  the  author,  in  a  paper  entitled, 
"The  Voluntary  and  Involuntary  Brain  Centers  Controlling 
the  Ocular  Muscles."  The  following  quotation  is  from  that 
paper : 

"There  is  one  basal  center  for  each  ocular  muscle,  and 
each  center  can  act  on  only  one  muscle.  The  basal  cen- 
ters are  all  under  the  control  of  the  fusion  faculty  of  the 
mind,  and  none  of  them  are  ever  called  on  to  discharge 
neuricity  unless  a  condition  exists  that  would  cause  diplo- 
pia." 

The  power  that  can  cause  harmonious  upward  rota- 
tion when  one  eye  is  hyperphoric  and  the  other  is  cata- 
phoric must  come  from  two  sources.     Volition  unlocks  the 


58  THE   BRAIN   CENTERS 

first  conjugate  center,  which  sends  an  equal  quantity  of 
neuricity  to  the  two  superior  recti;  the  fusion  faculty  of 
the  mind  unlocks  the  first  basal  center,  connected  with  the 
weaker  muscle,  which  sends  to  it  a  supplemental  quantity 
of  neuricity,  making  its  eye  move  as  fast  and  as  far  as  its 
fellow,  thus  preventing  diplopia. 

The  conjugate  centers  are  all  in  the  cortex,  probably  in 
the  anterior  part  of  the  motor  area.  Future  observers  will 
locate  these  centers  accurately.  There  are  nine  in  connec- 
tion with  the  recti  and  oblique  muscles,  one  connected  with 
the  ciliary  muscle,  and  one  with  the  sphincter  muscle  of 
the  iris.  There  must  also  be  a  conjugate  cortical  center 
for  the  two  muscles  that  elevate  the  upper  lids.  Fibers 
from  the  latter  center  help  to  compose  the  third  nerve ;  but 
in  the  plate  illustrating  the  third  nerve,  these  fibers,  and  the 
center  from  which  they  come,  will  not  be  included,  nor  will 
the  elevator  muscles  be  figured. 

The  conjugate  centers,  probably,  are  not  widely  sep- 
arated in  the  cortex,  but  their  exact  arrangement  in  the 
group  is  unknown.  In  the  illustrative  plates  to  follow,  all 
these  centers  are  represented  schematically,  and  they  are 
numbered  arbitrarily.  Those  connected  with  the  recti  mus- 
cles are  numbered  from  1  to  5,  and  those  connected  with 
the  obliques  are  numbered  from  6  to  9.  The  tenth  is  the  one 
connected  with  the  Muller  muscle  of  the  ciliary  body.  The 
eleventh  is  connected  with  the  sphincter  muscle  of  the  iris. 


AND   THE   OCULAR   MUSCLES.  59 

From  each  cortical  conjugate  center  go  two  fibers,  or 
two  sets  of  fibrils;  one  goes  to  a  single  muscle  on  the  cor- 
responding side,  the  other  crossing  the  median  line  goes  to 
a  single  muscle  on  the  opposite  side.  These  muscles  thus 
united  with  a  common  center,  constitute  a  pair.  Evidently 
the  centers  formed  in  the  cortex  of  one  hemisphere  exist  in 
duplicate  in  the  other  hemisphere,  and  each  duplicate  center 
must  have  a  connection  with  the  same  two  muscles.  To 
illustrate,  the  first  conjugate  center  in  the  left  cortex  is 
connected  with  the  two  superior  recti  and  supplies  them 
with  power.  The  first  conjugate  center  in  the  right  cortex 
must  have  a  similar  connection  with  the  two  superior  recti, 
but  this  center  sends  no  neuricity  to  these  muscles,  and 
therefore  does  not  excite  them  into  contractility. 

Two  centers,  one  on  each  side  of  the  brain,  connected 
with  each  pair  of  muscles,  and  only  one  of  these  centers 
active,  may  be  always  a  subject  for  disputation.  It  is  rea- 
sonable to  suppose  that,  at  the  time  of  birth,  one  of  these 
centers  stands  as  ready  to  effect  a  given  rotation  as  does 
the  other.  Why  one  should  become  active  and  the  other 
remain  inactive,  throughout  life,  must  be  determined  by 
some  pre-existing  condition,  and  not  by  chance.  I  It  is  not 
enough  to  say  that  in  right-handed  people  the  left  brain 
dominates,  and  in  left-handed  people  the  right  brain  dom- 
inates: for  the  condition  that  makes  the  left  brain  or  the 
right  brain  dominant,  also  makes  the  person  right-handed 


60  THE   BRAIN   CENTERS 

or  left-handed.  The  author  has  taught,  for  many  years, 
that  the  predetermining  condition  is  the  connection  that  the 
maculas  have  with  the  brain.  If  all  the  fibers  from  the  two 
maculas  meet  in  the  left  tract,  they  must  go  together  to 
the  left  cuneus ;  but  if  they  all  meet  in  the  right  tract,  they 
must  go  to  the  right  cuneus.  In  the  former  condition,  di- 
rect vision  would  excite  only  the  left  cuneus;  in  the  latter, 
direct  vision  would  excite  only  the  right  cuneus.  The  trans- 
mission of  all  macular  impressions  to  the  left  cuneus  es- 
tablishes, it  is  reasonable  to  suppose,  the  dominancy  of  the 
left  hemisphere,  especially  as  to  those  cortical  centers  that 
largely  depend  for  their  development  on  vision.  Even  the 
speech  center,  either  directly  or  indirectly,  becomes  fixed 
on  the  same  side.  The  same  should  be  said  of  the  right 
hemisphere,  when  all  macular  impressions  are  conveyed  to 
the  right  cuneus. 

The  hand  and  arm  centers  exist  in  both  hemispheres,  and 
both  are  developed,  usually  one  more  highly  than  the  other ; 
but  the  centers  in  the  left  brain  are  connected  with  the  right 
arm  only,  while  those  in  the  right  brain  are  connected  with 
the  left  arm  only.  The  right  and  left  hands  never  act  as 
one  organ. 

The  respiratory  muscles  exist  on  both  sides  of  the  body 
and  act  not  only  in  harmony,  but  simultaneously,  as  if  they 
constituted  a  single  organ.  The  centers  in  the  left  hemis- 
phere and  the  centers  in  the  right  hemisphere,  each  must 


AND   THE   OCULAR   MUSCLES.  61 

be  connected  with  two  respiratory  muscles,  one  on  either 
side  of  the  body;  and  each  of  these  muscles  must  re- 
ceive a  double  impulse,  one  from  its  center  in  the  right 
brain,  and  one  from  its  center  in  the  left  brain.  This 
is  made  evident  by  the  fact  that,  while  disease  or 
injury  of  one  side  of  the  brain  will  weaken  the  ac- 
tion of  the  muscles  of  respiration  on  both  sides,  it  will 
not  paralyze  them  on  one  side  and  leave  them  active  on 
the  other  side.  Like  the  centers  controlling  the  extremi- 
ties, the  centers  of  respiration  in  both  sides  of  the  brain 
are  active;  but  unlike  the  centers  controlling  the  extremi- 
ties, the  centers  of  respiration  in  each  side  have  connection 
with  muscles  on  both  sides  of  the  chest.  The  muscles  of  the 
chest  are  like  those  of  the  eye  in  that  each  is  connected  with 
two  centers,  one  in  either  hemisphere ;  but  while  the  former 
are  acted  on  by  both  centers,  the  latter  receive  neuricity 
from  centers  on  only  one  side  of  the  brain. 

In  the  illustrative  plates  to  be  studied,  all  the  active  con- 
jugate cortical  centers,  except  the  fifth,  are  situated  in  the 
left  hemisphere,  and  all  the  non-acting  centers,  except  the 
fifth,  are  placed  in  the  right  hemisphere.  The  active  cen- 
ters are  represented  by  larger  circles,  and  the  non-active 
by  smaller  circles.  The  conjugate  centers  known  to  be 
under  the  control  of  volition  are  each  crossed  by  two  paral- 
lel lines.  The  sixth  and  seventh  conjugate  centers  exist 
solely  in  the  interest  of  binocular  single  vision,  and  are  sup- 


62  THE    BRAIN    CENTERS 

posed  to  be  under  the  control  of  the  fusion  faculty  of  the 
mind.  The  circles  representing  these  are  not  crossed  by 
parallel  lines. 

The  basal  centers  connected  with  the  twelve  extrinsic 
ocular  muscles  all  exist  in  the  interest  of  binocular  single 
vision,  each  is  connected  with  only  one  muscle,  and  they 
are  all  under  the  control  of  the  fusion  faculty  of  the  mind. 
Unless  some  condition  exists  or  arises  that  would  cause 
diplopia,  these  centers  are  ever  inactive,  their  normal  state 
being  one  of  rest.  Their  location  is  on  either  side  of  the 
median  line  beneath  the  aqueduct  of  Sylvius  and  in  the  an- 
terior part  of  the  floor  of  the  fourth  vertical.  In  the  plates 
to  follow,  the  basal  centers  are  represented  schematically, 
and  they  are  numbered  in  harmony  with  the  numbering  of 
the  conjugate  cortical  centers.  They  exist  in  pairs,  but 
work  independently.  They  all  stand  ready  always  to  dis- 
charge neuricity  that  images  may  be  fused,  but  a  discharge 
from  a  single  center  can  affect  only  a  single  muscle. 

There  are  doubtless  basal  centers  for  Muller  muscles  of 
the  ciliary  body  and  for  the  sphincter  muscles  of  the  iris, 
and  these  are  represented  in  each  plate.  The  former  are 
right  and  left  tenth  basal  centers,  and  the  latter  are  right 
and  left  eleventh  basal  centers.  In  emmetropia,  and  in 
ametropia,  the  error  being  equal  in  the  two  eyes,  the  tenth 
basal  centers  would  have  nothing  to  do.  When  there  is 
unequal  refraction  the  muscle  that  must  exert  the  greater 


AND   THE   OCULAR    MUSCLES.  63 

power  for  the  formation  of  a  sharp  image  must  receive 
supplemental  neuricity  from  its  basal  center;  for  the  tenth 
conjugate  center,  like  the  conjugate  centers  that  control  the 
extrinsic  muscles,  sends  neuricity  in  equal  quantities  to  the 
two  ciliary  muscles,  equal  contraction  resulting.  Again, 
the  necessity  for  the  tenth  basal  centers  may  be  understood 
by  conceding  the  possibility  that  the  ciliary  muscles  may  be 
endowed  with  unequal  tonicity.  When  this  is  true  the  tenth 
conjugate  center  cannot  excite  equal  contraction,  and  sup- 
plemental neuricity  must  come  from  the  basal  center  con- 
nected with  the  weaker  muscle. 

The  right  and  left  eleventh  basal  centers  are  shown  in  the 
plates,  as  is  also  the  eleventh  conjugate  center.  These  cen- 
ters are  connected  with  the  sphincter  muscles  of  the  iris. 
If  the  sphincters  are  of  equal  tonicity  the  conjugate  center 
alone  will  act ;  but  if  they  differ  in  tonicity,  the  muscle  that 
is  weaker  must  have  supplemental  neuricity  from  its  basal 
center. 

The  extrinsic  and  intrinsic  muscles  of  the  eye  have  their 
connection  with  the  conjugate  and  basal  centers  through 
the  medium  of  three  pairs  of  nerves — the  third,  the  fourth 
and  the  sixth  cranial  nerves.  Plate  I.  represents  the  con- 
nection of  brain  centers  and  muscles  through  the  medium 
of  the  right  third  nerve.  A  study  of  this  plate  will  show 
that  the  third  nerve  is  nothing  more  nor  less  than  a  cable 
composed  of  many  insulated  nerve  fibers,  which  connect 


64 


THE    BRAIN    CENTERS 

2      \  12 


AND   THE   OCULAR    MUSCLES. 

*     ?  12 


65 


66  THE    BRAIN    CENTERS 

eight  active  conjugate  centers  and  six  basal  centers  with 
three  recti  muscles,  one  oblique  muscle,  the  ciliary  muscle 
and  the  sphincter  of  the  iris.  The  left  side  of  that  part  of 
the  plate  representing  the  brain  is  the  dominant  hemisphere. 
From  each  conjugate  center  two  lines  are  drawn,  one  stop- 
ping in  mid-brain,  the  other  extending  on,  by  way  of  the 
basal  centers,  to  help  form  the  third  nerve  cable.  The  line 
stopping  midway  between  conjugate  and  basal  centers  rep- 
resents the  fiber,  or  set  of  fibrils,  that  would  help  to  form 
the  left  third  nerve,  which  is  shown  in  Plate  II. 

The  first  conjugate  center,  which  controls  the  two  su- 
perior recti,  sends  a  fiber,  or  set  of  fibrils,  to  the  left  first 
basal  center,  thence  across  to  the  right  first  basal  center, 
thence  on  in  the  sheath  of  the  right  third  nerve  to  the  right 
superior  rectus.  In  the  right  first  basal  center  begins  a 
neuron  whose  insulated  axone  passes  within  the  third  nerve 
to  the  right  superior  rectus.  Over  the  former  line  travels 
the  volitional  impulse;  over  the  latter  travels  the  fusion 
impulse. 

The  second  conjugate  center,  which  controls  the  two  in- 
ferior recti,  has  two  fibers,  or  sets  of  fibrils,  one  to  reach 
its  destination  through  the  right  third  nerve  and  the  other 
through  the  left  third  nerve.  The  former  passes  to  the  left 
second  basal  center,  thence  across  to  the  right  second  basal 
center  and  thence  in  the  right  third  nerve  to  the  right  in- 
ferior rectus.     The  right  second  basal  center  sends  its  con- 


AND   THE   OCULAR    MUSCLES.  67 

necting  line,  in  the  third  nerve  cable,  to  the  right  inferior 
rectus. 

The  third  conjugate  center,  or  the  convergence  center,  is 
connected  with  both  interni.  The  fiber,  or  set  of  fibrils,  to 
connect  with  the  right  interims,  passes  down  to  the  left 
third  basal  center,  thence  across  to  the  right  third  basal 
center,  thence  to  help  from  the  body  of  the  right  third 
nerve,  on  to  its  destination  in  the  right  internus.  The 
right  third  basal  center  sends  a  connecting  line  through  the 
right  third  nerve  to  the  right  internus. 

The  fifth  conjugate  center  in  the  right  hemisphere  is 
connected  with  the  right  internus  through  the  right  third 
nerve  and  with  the  left  externus  through  the  left  sixth 
nerve.  The  former  connection  is  shown  in  Plate  I.  and  the 
latter  is  shown  in  Plate  VI. 

The  seventh  conjugate  center  is  connected  with  both  in- 
ferior obliques.  The  connection  with  the  right  inferior 
oblique  is  by  way  of  the  left  seventh  basal  center,  across 
to  right  seventh  basal  center,  thence  on  in  the  body  of  the 
right  third  nerve  to  the  right  inferior  oblique.  The  right 
seventh  basal  center  has  its  independent  connection  with 
the  same  muscle,  by  way  of  the  same  nerve. 

The  ninth  conjugate  center  is  connected  with  the  right  in- 
ferior oblique  and  the  left  superior  oblique,  the  former  being 
shown  in  Plate  I.  and  the  latter  in  Plate  IV. 

The  tenth  conjugate  center  is  connected  with  the  Muller 


68  THE    BRAIN    CENTERS 

muscle  of  accommodation  in  each  eye.  Its  connection  with 
the  right  eye  is  by  way  of  the  left  tenth  basal  center,  across 
to  the  right  tenth  basal  center,  thence  on,  through  the  right 
third  nerve  to  its  destination.  The  right  tenth  basal  cen- 
ter has  its  connecting  fibers  passing  down  in  the  right  third 
nerve  to  the  Muller  muscle  of  the  right  eye. 

The  eleventh  conjugate  center  is  connected  by  means  of 
the  right  and  left  third  nerves  with  the  sphincter  muscles 
of  the  iris  of  both  the  right  and  left  eyes,  the  right  con- 
nection being  shown  in  Plate  I.  and  the  left  connection 
being  shown  in  Plate  II.  The  basal  center  connections  are 
likewise  shown  in  the  two  plates. 

A  glance  at  Plate  I.  will  show  that  the  third  nerve  cable 
is  composed  of  insulated  fibers  from  eight  of  the  eleven 
active  conjugate  cortical  centers;  that  the  fibers  from  seven 
of  these  centers  cross  the  median  line  to  help  form  the 
right  third  nerve,  the  only  non-crossing  fibers  coming  from 
the  fifth  conjugate  center.  The  broken  lines  from  the  cor- 
responding eight  inactive  centers  are  intended  to  show  a 
connection  between  these  centers  and  the  muscles  controlled 
by  the  eight  active  centers. 

Plate  I.  also  shows  that  the  right  third  nerve  has  in  it 
insulated  fibers  from  six  of  the  eight  right  basal  centers. 
None  of  these  basal  fibers  have  crossed. 

Plate  I.  is  not  a  complete  picture  of  the  brain  and  muscle 
connections  composing  the  right  third  nerve.     In  each  third 


AND   THE   OCULAR    MUSCLES.  6D 

nerve  there  are  fibers  from  a  conjugate  center  controlling 
the  elevator  muscles  of  the  upper  lids.  There  are  also  fibers 
in  each  third  nerve  from  the  superior  cervical  sympathetic 
ganglion.  Some  of  the  fibers  from  this  ganglion  are  prob- 
ably distributed  to  the  Bowman  fibers  of  the  ciliary  muscle 
and  others  to  the  radiating  fibers  of  the  iris.  The  impulse 
sent  over  the  former  fibers,  in  all  probability,  causes  a  tilt- 
ing of  the  lens  for  correcting  a  corneal  astigmatism. 

No  attempt  is  made  in  Plates  I.  and  II.  to  show  the  ciliary 
ganglion  through  which  pass  all  the  short  ciliary  fibers  of 
the  third  nerve  on  their  way  to  the  muscles  in  the  ciliary 
body  and  in  the  iris. 

Plate  II.  shows  that  the  left  third  nerve  cable  is  com- 
posed of  fibers  from  eight  active  conjugate  centers,  all  in 
the  left  hemisphere  and  from  six  basal  centers,  also  in 
the  left  hemisphere.  The  fifth  and  ninth  conjugate  cen- 
ters, which  send  axones  through  the  right  third  nerve,  have 
none  in  the  left  third  nerve,  the  fourth  and  eighth  conju- 
gate centers  taking  their  places.  Only  the  left  basal  cen- 
ters send  axones  into  the  left  third  nerve.  All  of  the  non- 
active  conjugate  centers,  except  the  fifth,  sixth  and  ninth, 
doubtless  have  axones  in  the  left  third  nerve.  None  of  the 
"live"  fibers  constituting  the  left  third  nerve  cable  are  con- 
nected with  the  centers  in  the  right  hemisphere,  hence  there 
has  been  no  crossing.  This  is  in  marked  contrast  with  the 
fibers  forming  the  right  third  nerve.     This  arrangement  of 


70 


THE   BRAIN   CENTERS 


S«   tl 


AND   THE   OCULAR   MUSCLES. 
2  1  12 


71 


72  THE   BRAIN    CENTERS 

fibers  would  be  reversed  in  a  person  whose  right  brain  is 
dominant — in  a  person  whose  maculas  are  wholly  connected 
with  the  right  cuneus. 

Of  the  eight  conjugate  centers  that  send  fibers  through 
the  third  nerve  cables  to  the  superior,  inferior  and  internal 
recti  and  to  the  inferior  oblique,  not  more  than  three  are 
ever  active  at  the  same  time,  and  in  some  of  the  binocular 
rotations  all  these  centers  except  one  will  be  in  a  state  of 
rest.     But  this  will  be  clearly  shown  in  subsequent  plates. 

THE    FOURTH    PAIR    OF    NERVES. 

Plate  III.  shows  the  conjugate  and  basal  centers  whose 
axones  form  the  right  fourth  nerve,  which  is  also  a  cable. 
The  sixth  conjugate  center  sends  fibers  to  both  superior 
obliques.  The  fiber,  or  set  of  fibrils,  destined  for  the  left 
superior  oblique,  are  carried  in  the  plate  only  part  of  the 
way  to  the  sixth  basal  center,  but  the  fiber  to  connect  with 
the  right  superior  oblique  is  carried  down  to  the  left  sixth 
basal  center,  thence  across  to  the  right  sixth  center,  thence 
on  in  the  right  fourth  nerve  to  its  termination  in  the  su- 
perior oblique.  Starting  in  the  right  sixth  basal  center  is 
an  axone  that  helps  to  form  the  right  fourth  nerve,  finally 
ending  in  the  right  superior  oblique. 

From  the  eighth  conjugate  center  goes  a  fiber,  or  set  of 
fibrils,  down  to  the  left  sixth  basal  center,  thence  across  to 
the  right  sixth  basal  center,  thence  in  the  right  fourth 


AND   THE   OCULAR    MUSCLES.  73 

nerve  to  the  right  superior  oblique.  The  other  fiber  from 
this  center,  as  shown  in  Plate  II. ,  helps  to  form  the  left  third 
nerve,  and  ends  in  the  left  inferior  oblique. 

Plate  IV.  shows  the  conjugate  and  basal  centers  whose 
axones  form  the  left  fourth  nerve.  The  conjugate  centers 
are  the  sixth  and  ninth,  and  the  basal  center  is  the  left 
sixth.  There  are  no  "live"  crossed  fibers  in  the  left  fourth 
nerve. 

THE  SIXTH   PAIR  OF  NERVES. 

Plate  V  shows  that  the  fourth  conjugate  center  and  the 
right  fourth  basal  center  have  "live"  axones  in  the  right 
sixth  nerve,  which,  too,  is  a  cable.  The  silent  fourth  con- 
jugate center  sends  axones,  as  shown  by  the  broken  line,  to 
the  right  fourth  basal  center,  thence  in  the  right  sixth  nerve 
to  the  right  externus.  The  fiber  represented  by  the  broken 
line  conveys  no  neuricity,  for  its  center  discharges  none. 
The  right  externus  has  only  two  sources  of  neuricity,  the 
fourth  conjugate  center  and  the  right  fourth  basal  center. 
The  former  center  is  active  only  in  the  right  sweep  of  the 
eye,  and  the  latter  is  active  only  in  the  interest  of  binocular 
single  vision. 

Plate  VI.  shows  that  axones  from  the  fifth  conjugate  cen- 
ter and  from  the  left  fourth  basal  center  form  the  left  sixth 
nerve.  The  former  is  active  only  in  the  left  sweep  of  the 
eye,  and  the  latter  acts  only  in  the  interest  of  binocular 
single  vision. 


74 


THE   BRAIN   CENTERS 

*     \  12 


AND   THE   OCULAR   MUSCLES. 

2 


75 


76  THE   BRAIN    CENTERS 

EMMETROPIA — ORTHOPHORIA. 

Plates  VII.  to  XVI.  inclusive  are  intended  to  show  that  in 
emmetropic-orthophoric  eyes,  regardless  of  the  point  of 
view,  no  basal  center  is  ever  called  on  to  discharge  neu- 
ricity.  These  plates  likewise  show  that,  in  such  cases,  rest- 
fulness  is  the  normal  state  of  all  the  basal  centers. 

Plate  VII.  represents  the  restfulness  of  all  brain  centers, 
the  conjugate  and  the  basal,  and  the  consequent  restful 
state  of  all  the  eye  muscles,  extrinsic  and  intrinsic,  when 
the  head  is  in  the  primary  position  and  the  emmetropic- 
orthophoric  eyes  are  fixed  on  an  object  at  practical  infinity 
and  in  the  line  of  intersection  of  the  extended  median  and 
horizontal  fixed  planes  of  the  head.  This  restfulness  of 
brain  centers  and  muscles  could  not  be  better  represented 
than  by  leaving  out  their  axonic  connections.  If  a  brain 
center  is  not  discharging  neuricity,  the  muscle  is  not  con- 
tracting, and  the  axone  is  not  alive.  The  condition  is  as 
if  the  axone  were  absent. 

From  this  restful  state  of  brain  and  muscle,  the  eyes  may 
be  moved,  or  rotated,  instantly  into  any  of  the  positions 
represented  in  Plates  VIII.  to  XVI.,  as  a  result  of  the  action 
of  volition  on  the  respective  conjugate  brain  centers,  the 
basal  brain  centers  remaining  inactive.  Each  of  these 
plates  represents  the  eyes  ready  to  begin  the  respective  ro- 
tations, and  not  the  completed  act. 


AND    THE   OCULAR   MUSCLES.  77 

Plate  VIII.  represents  the  act  of  convergence  of  emme- 
tropic-orthophoric  eyes,  the  associated  action  of  the  accom- 
modation, and  the  brain  centers  that  have  effected  these 
changes  from  the  restful  state  shown  in  Plate  VII.  The 
head  is  still  in  the  primary  position,  and  the  near  object  is 
in  the  line  of  intersection  of  the  extended  median  and  hori- 
zontal planes.  Volition  discharges  the  third  conjugate  cen- 
ter and  causes  a  flow  of  an  equal  quantity  of  neuricity  to 
each  of  the  two  interni,  which,  responding  with  equal 
power,  converge  the  visual  axes  to  the  point  of  fixation. 
Simultaneously,  volition  unlocks  the  tenth  conjugate  center, 
which  sends  an  equal  quantity  of  neuricity  to  each  of  the 
Muller  muscles  of  accommodation,  thus  causing  a  perfect 
focusing,  on  each  retina,  of  the  rays  of  light  coming  from 
the  point  of  fixation.  The  whole  work  of  changing  the 
eyes  from  the  restful  state  shown  in  Plate  VII.  to  the  state 
of  convergence-accommodation  activity,  has  been  accom- 
plished by  the  internal  recti,  under  the  influence  of  the  third 
conjugate  center,  and  by  the  Muller  muscles  under  the  influ- 
ence of  the  tenth  conjugate  center.  The  activity  of  the  mus- 
cles, and  of  the  centers  exciting  them,  is  shown  by  the  lines 
drawn  from  the  two  conjugate  centers  through  the  proper 
basal  centers  to  the  muscles.  The  absence  of  lines  extending 
from  other  conjugate  centers  to  other  muscles  is  intended  to 
show  the  restful  state  of  both.  The  absence  of  axones  ex- 
tending from  right  and  left  third  and  the  right  and  left  tenth 


78 


THE   BRAIN   CENTERS 


1      2 


AND   THE   OCULAR    MUSCLES. 


79 


80  THE    BRAIN    CENTERS 

basal  centers,  shows  that  these  centers  are  not  concerned  in 
the  act  of  convergence-accommodation  of  emmetropic-or- 
thophoric  eyes. 

To  avoid  confusion,  no  lines  have  been  drawn  from  the 
eleventh  conjugate  center  to  the  sphincter  muscles  of  the 
iris,  but  it  must  be  stated  that,  in  accommodation,  the  pupils 
are  always  made  smaller  because  of  a  discharge  of  neu- 
ricity  from  this  center  to  its  proper  muscles. 

The  third  and  the  tenth  conjugate  centers  are  most  inti- 
mately related,  in  action,  and  this  relationship  is  probably 
co-extensive  with  life.  For  every  accommodative  dioptre 
of  neuricity  discharged  by  the  tenth  conjugate  center,  a  cor- 
responding convergence  dioptre  of  neuricity  will  be  dis- 
charged by  the  third  conjugate  center.  If  the  muscles  sup- 
plied by  these  centers  are  normal  in  tonicity,  there  will  be 
normal  contraction  from  a  normal  stimulus. 

It  is  a  mistake  to  conclude  that  emmetropic  and  ortho- 
phoric  eyes  for  distance  can  give  no  trouble  in  near  seeing. 
Trouble  may  come  from  either  one  of  two  conditions  of 
Muller's  muscles :  First,  these  muscles,  in  emmetropic  eyes, 
may  be  wanting  in  tonicity;  secondly,  they  may  have  an 
excess  of  tonicity.  If  wanting  in  tonicity  they  will  require 
an  excess  of  neuricity  for  the  accomplishment  of  a  given 
work.  If  the  interni,  in  such  a  case,  have  normal  tonicity, 
the  right  and  left  fourth  basal  centers  will  be  excited  into 
action   whenever  an   accommodation-convergence  effort   is 


AND   THE   OCULAR    MUSCLES.  81 

made.  Such  a  state  is  shown  by  esophoria  in  the  near, 
when  there  is  orthophoria  for  distance.  This  pseudo- 
esophoria  is  caused  by  the  fact  that  the  weak  Muller  mus- 
cles require  four  accommodative  diopters  of  neuricity  to 
effect  a  3  D.  change  in  the  lenses ;  an  associated  four  con- 
vergence dioptres  of  neuricity,  sent  to  the  normal  interni, 
would  cause  an  excess  of  convergence,  to  prevent  which  the 
right  and  left  fourth  basal  centers  would  be  excited  by  the 
fusion  faculty  of  the  mind.  They  would  be  made  to  dis- 
charge enough  neuricty  to  their  respective  externi  to  coun- 
teract the  excessive  convergence.  The  excitation  of  these 
basal  centers  would  be  kept  up  only  during  accommodation- 
convergence.  The  centers  acting  in  this  condition  are 
shown  in  Plate  XVIII. 

In  the  second  place,  when  the  Muller  muscles  have  an 
excess  of  tonicity  it  may  take  only  two  accommodative 
dioptres  of  neuricity  to  effect  a  3  D.  change  in  the  lenses. 
The  associated  two  convergence  dioptres  of  neuricity  from 
the  third  conjugate  center  would  not  effect  sufficient  con- 
vergence, hence  the  right  and  left  third  basal  centers,  under 
the  influence  of  the  fusion  faculty,  must  furnish  supple- 
mental neuricity  to  the  normal  interni.  The  centers  ex- 
cited in  such  a  case  are  shown  in  Plate  XXII.  The  excited 
right  and  left  third  basal  centers  become  quiet  the  moment 
accommodation  ceases,  as  is  true  of  the  right  and  left 
fourth  basal  centers  when  the  Muller's  muscles  are  lacking 


82  THE   BRAIN   CENTERS 

in  tonicity.  Such  eyes,  though  emmetropic  and  orthophor- 
ia would  cause  trouble,  but  only  when  used  in  reading  or 
other  near  work. 

The  pseudo-esophoria  in  the  first  case  and  the  pseudo- 
exophoria  in  the  second  case,  must  be  counteracted,  and 
the  effort  made  by  the  basal  centers  for  this  purpose,  is 
doubtless,  the  source  of  the  symptoms  attending  the  near 
use  of  such  eyes.  The  treatment  of  such  cases  should  be 
directed  towards  the  relief  of  the  basal  centers,  whose  nor- 
mal state  is  rest,  and  not  action.  The  pseudo-esophoria 
can  be  cured  in  one  of  two  ways :  First,  by  rhythmic  exer- 
cise of  the  ciliary  muscles,  increasing  their  tonicity  to 
the  normal ;  second,  by  allowing  the  patient,  though  young, 
to  wear  convex  lenses  of  proper  strength  for  near  work. 
Relief  comes  from  either  plan  of  treatment,  but  the  former 
should  be  adopted.  Likewise  the  pseudo-exophoria  may  be 
treated  in  one  of  two  ways :  First,  exercise  of  the  interni, 
by  prisms,  or  by  the  candle  method,  so  as  to  develop  in  them 
an  excess  of  tonicity;  second,  by  permitting  the  patient, 
though  emmetropic,  to  wear  concave  lenses  of  suitable 
strength,  in  near  work  only.  Either  plan  may  bring  relief, 
but  the  former  should  be  adopted. 

THE  VERSIONS. 

Plate  IX.  is  intended  to  show  the  activity  of  brain  and 
muscles  in  effecting  the  right  sweep  of  the  eyes — right  ver- 


AND    THE   OCULAR    MUSCLES.  83 

sion.  The  rotation  plane  lies  in  the  fixed  horizontal  plane 
of  the  head ;  the  visual  axes  are  practically  parallel ;  the 
only  active  muscles  in  this  rotation  are  the  right  externus 
and  the  left  internus;  and  the  center  that  controls  them  is 
the  fourth  conjugate.  The  lines  extending  from  this  center 
to  these  muscles  represent  the  axones  down  which  the  neu- 
ricity  travels,  in  equal  quantities,  to  the  two  muscles  that 
have  equal  tonicity.  The  basal  centers  and  all  other  conju- 
gate centers  are  perfectly  quiet.  The  antagonism  of  the 
right  internus  and  of  the  left  externus  is  only  the  antag- 
onism of  tonicity. 

Plate  X.  illustrates  left  version,  which  is  effected  by  the 
left  externus  and  the  right  internus  under  the  influence  of 
the  fifth  conjugate  center,  the  visual  axes  being  practically 
parallel.  All  other  muscles  and  centers,  both  conjugate 
and  basal,  are  inactive. 

When  the  visual  axes  are  converged  as  in  reading,  the 
right  and  left  versions  are  effected  by  the  fourth  and  fifth 
conjugate  centers  respectively;  and  the  other  conjugate 
centers  simultaneously  active  are  the  third  and  tenth.  A 
combination  of  Plates  VIII.  and  IX.  would  show  the  active 
muscles  and  the  excited  centers  in  right  version  as- 
sociated with  convergence  and  accommodation.  A  com- 
bination of  Plates  VIII.  and  X.  would  show  the  active 
muscles  and  excited  centers  in  the  left  sweep  of  convergent' 
eyes.     In  reading,  if  the  head  is  tilted  forward  so  that  the 


84 


THE   BRAIN   CENTERS 

2       1  12 


AND   THE   OCULAR   MUSCLES. 


85 


86  THE   BRAIN   CENTERS 

plane  of  rotation  shall  lie  in  the  extended  horizontal  plane 
of  the  head,  the  muscles  engaged  are  the  two  ciliary,  the 
two  interni,  the  right  externus  and  the  left  internus,  and 
the  left  externus  and  the  right  internus;  and  the  centers 
controlling  the  action  of  these  muscles  are  the  third,  fourth, 
fifth  and  tenth  conjugate  centers.  If  the  plane  of  rotation 
falls  below  the  extended  horizontal  plane  of  the  head,  as  it 
must  when  one  reads  lying  down,  four  additional  muscles, 
the  two  inferior  recti  and  the  two  superior  obliques,  must 
join  in  the  work,  and  two  additional  conjugate  centers, 
the  second  and  the  sixth,  must  become  active.  The  natural 
pose  of  the  head  in  reading  or  other  near  work  is  such  as 
to  cause  a  minimum  excitation  of  the  second  and  the  sixth 
conjugate  centers.  There  should  be  no  reading  in  the  re- 
cumbent posture,  even  when  one  is  well  and  strong.  The 
brain  and  muscle  work  expended  when  one  reads  while  re- 
cumbent is  shown  by  a  combination  of  Plates  VIII.,  IX.,  X. 
and  XII. 

The  upward  sweep  of  the  eyes — superversion — is  effected 
by  four  muscles,  the  two  superior  recti  and  the  two  inferior 
obliques.  Plate  XL  shows  that  this  rotation  of  orthophoric 
eyes  is  effected  by  the  first  and  seventh  conjugate  centers, 
and  that  all  other  centers,  both  conjugate  and  basal,  are  at 
rest. 

Plate  XII.  shows  that  subversion  is  effected  by  the  two 
inferior  recti  and  the  superior  obliques  under  the  control 


AND    THE   OCULAR    MUSCLES.  87 

of  the  second  and  sixth  conjugate  centers  respectively, 
and  that,  in  vertical  orthophoria,  all  other  centers  are  quiet. 
No  error  of  refraction  has  any  influence  over  the  superior 
or  inferior  recti,  or  the  conjugate  or  basal  centers  controll- 
ing them. 

Plate  XIII.  shows  the  conjugate  brain  centers  and  the 
muscles  that  are  concerned  in  the  rotations  up  and  to  the 
right,  the  visual  axes  being  parallel.  The  visual  axis  of 
the  right  eye  is  carried  up  and  to  the  right  in  a  plane  com- 
mon to  the  first  and  second  points  of  view  and  the  center 
of  rotation,  by  the  externus  and  superior  rectus;  and  the 
visual  axis  of  the  left  is  moved  in  another  plane  common  to 
the  first  and  second  points  of  views  and  its  center  of  rota- 
tion, by  the  internus  and  superior  rectus.  The  first  and 
fourth  conjugate  centers  act  on  their  respective  muscles  as 
if  they  constituted  one  center,  and  the  four  muscles  act  as 
if  they  were  but  two — one  for  each  eye — and  the  rotation 
plane  of  each  one  included  the  center  of  rotation  of  its 
eye  and  the  first  and  second  points  of  view.  The  four  recti 
concerned,  being  normal  in  tonicity,  make  no  demand  on 
their  respective  basal  centers.  This  oblique  rotation  could 
not  be  effected  without  interference  with  the  all-important 
relationship  of  the  vertical  axes  of  the  eyes  and  the  median 
plane  of  the  head,  except  for  nature's  provision  for  prevent- 
ing it.  The  torsioning  of  both  eyes  would  be  to  the  right, 
but  this  is  prevented  by  the  eighth  conjugate  center,  which 


88 


THE   BRAIN   CENTERS 

11  1     ? 


FLAIZXI 


AND   THE   OCULAR   MUSCLES. 
2         1  12 


89 


90 


THE   BRAIN   CENTERS 
*        I  1         ? 


AND   THE   OCULAR    MUSCLES. 

t     J  I? 


91 


92  THE   BRAIN   CENTERS 

sends  neuricity  to  the  right  superior  oblique  and  left  in- 
ferior oblique,  their  resulting  contraction  keeping  the  ver- 
tical axes  parallel  with  the  median  plane  of  the  head,  while 
the  first  and  fourth  conjugate  centers  are  effecting  the 
oblique  rotations.  The  six  acting  muscles  are  opposed  by 
the  other  six,  but  the  antagonism  is  that  of  tonicity  and 
not  contractility,  hence  all  conjugate  centers,  except  the 
first,  fourth  and  eighth,  are  at  rest,  and  not  a  basal  center 
is  active. 

Plate  XIV.  represents  the  active  centers  and  muscles  that 
effect  rotations  of  the  two  eyes  down  and  to  the  left.  A 
comparison  of  this  plate  with  Plate  XIII.  will  show  that 
the  same  kind  of  torsioning  results  from  simultaneous  ac- 
tion of  the  second  and  fifth  conjugate  centers,  as  that  caused 
by  the  combined  action  of  the  first  and  fourth  conjugate 
centers,  for  the  torsioning  in  each  is  prevented  by  the  eighth 
conjugate  center. 

Plate  XV.  illustrates  rotation  upward  and  to  the  left  by 
the  action  of  the  first  and  fifth  conjugate  centers  on  the 
two  superior  recti  and  on  the  left  externus  and  right  in- 
ternus,  respectively.  The  torsioning  that  would  be  to  the 
left  is  prevented  by  the  action  of  the  ninth  conjugate  center 
on  the  left  superior  and  right  inferior  obliques.  In  this, 
as  in  all  oblique  rotations  of  emmetropic-orthophoric  eyes, 
the  work  is  accomplished  by  six  muscles  under  the  influ- 


AND   THE   OCULAR    MUSCLES.  93 

ence  of  three  conjugate  centers,  all  other  muscles  and  cen- 
ters being  free  from  activity. 

Plate  XVI.  shows  rotations  of  the  two  eyes  down  and 
to  the  right.  The  centers  that  cause  this  rotation  are  the 
second  and  fourth  conjugate,  and  the  torsioning  that  would 
occur  is  prevented  by  the  action  of  the  ninth  conjugate 
center  on  the  left  superior  and  right  inferior  obliques.  A 
comparison  of  Plates  XV.  and  XVI.  will  show  that  the  tor- 
sioning of  both  eyes  would  be  to  the  left  in  oblique  rotations 
up  and  to  the  left  and  down  and  to  the  right,  for  in  each 
case  it  is  prevented  by  the  action  of  the  ninth  conjugate 
center  on  the  left  superior  and  right  inferior  obliques. 

EMMETROPIA  AND  HETEROPHORIA. 

Esophoria. — Plate  XVII.  represents  a  pair  of  esophoric- 
emmetropic  eyes  looking  straight  ahead  at  a  point  at  prac- 
tical infinity,  the  head  being  in  the  primary  position.  The 
tonicity  of  the  interni  being  greater  than  the  tonicity  of  the 
externi,  the  visual  axes  would  tend  to  cross  before  reaching 
the  point  to  be  fixed.  Such  crossing  would  double  the 
point.  To  prevent  diplopia  the  fusion  faculty  of  the  mind 
unlocks  the  right  and  left  fourth  basal  centers  and  the  dis- 
charged neuricity  excites  just  enough  contractility  of  the 
two  externi  to  neutralize  the  tonicity  of  the  interni.  No 
other  brain  centers,  either  basal  or  conjugate,  are  active, 
and  all  the  muscles  execpt  the  externi  are  at  rest. 

Plate  XVIII.  shows  the  same  pair  of  eyes  in  the  act  of 


94 


THE   BRAIN   CENTERS 

1     \  12 


AND   THE   OCULAR    MUSCLES. 


95 


96  THE   BRAIN   CENTERS 

accommodation-convergence.  A  contrast  of  this  plate  with 
Plate  VIII.  will  show  that  the  only  difference  between  ac- 
commodation-convergence of  orthophoric  and  esophoric 
eyes,  is  that,  in  the  latter,  the  right  and  left  fourth  basal 
centers  must  act  on  their  respective  externi  to  prevent  the 
diplopia  which  would  result  if  the  interni  were  allowed  to 
cross  the  visual  axes  too  soon. 

Plate  XIX.  shows  the  same  pair  of  eyes  making  right 
version,  under  the  influence  of  the  fourth  conjugate  center, 
the  visual  axes  being  parallel.  By  contrasting  this  plate 
with  Plate  IX.,  one  can  readily  see  the  additional  work  the 
brain  must  do  in  effecting  the  right  sweep  of  esophoric  eyes, 
above  what  it  has  to  do  in  rotating  orthophoric  eyes  in  the 
same  direction.  In  Plate  IX.  the  externi  and  the  interni 
have  the  same  tonicity,  hence  the  equally  divided  impulse 
from  the  fourth  conjugate  center  will  make  the  one  eye 
move  as  fast  and  as  far  as  the  other.  In  Plate  XIX.  the  left 
internus  has  greater  tonicity  than  the  right  externus.  The 
equally  divided  impulse  from  the  fourth  conjugate  center 
would  make  the  strong  left  internus  move  its  eye  faster  and 
further  than  the  weak  right  externus  would  rotate  its  eye. 
The  lagging  behind  of  the  right  eye  would  cause  diplopia, 
to  prevent  which  the  right  fourth  basal  center  discharges 
supplemental  neuricity  to  the  weak  right  externus,  thus 
compelling  it  to  move  the  right  eye  in  harmony  with  the  left. 

Plate  XX.  shows  the  same  pair  of  eyes  in  the  effort  to 


AND   THE   OCULAR    MUSCLES.  97 

rotate  to  the  left — left  version.  Comparing  this  plate  with 
Plate  X.,  it  will  be  seen  in  the  latter  that  no  basal  center 
is  excited  in  left  version  of  orthophoric  eyes,  while  in  the 
former  plate  it  is  made  plain  that  the  left  fourth  basal 
center  must  send  neuricity  to  the  weak  left  externus  to 
supplement  that  coming  from  the  fifth  conjugate  center, 
in  order  that  the  weak  externus  may  make  its  eye  move  in 
harmony  with  the  right  eye,  whose  internus  is  strong. 

With  head  erect  and  eyes  fixed  on  a  point  in  line  of  inter- 
section of  the  extended  median  and  horizontal  planes  of  the 
head,  at  practical  infinity,  the  muscles  of  orthophoric  eye 
are  all  at  rest,  for  no  brain  center,  either  conjugate  or  basal, 
is  discharging  neuricity;  but  if  the  eyes  are  esophoric,  the 
right  and  left  fourth  basal  centers  are  forced,  by  the  fusion 
faculty,  to  discharge  neuricity  to  their  respective  externi, 
which  are  kept  in  a  constant  state  of  contraction  to  prevent 
diplopia.  In  the  right  and  left  sweep  of  orthophoric  eyes 
volition  alone  acts,  and  on  the  fourth  and  fifth  conjugate 
centers  r«*spectively ;  but  in  the  same  rotations  of  esophoric 
eyes  volition  alone  would  fail.  To  effect  harmonious  right 
version,  the  fusion  faculty  of  the  mind  aids  volition  by 
acting  on  the  right  fourth  basal  center;  and  the  same  aid 
is  rendered  in  left  version  by  the  fusion  faculty  acting  on 
the  left  fourth  basal  center. 

Volition  unaided  effects  accommodation  and  convergence 
of  emmotropic-orthophoric  eyes;  but  in  esophoria,  volition 


98 


THE   BRAIN    CENTERS 

*     !  I 


AND    THE    OCULAR    MUSCLES. 


99 


\      2 


100 


THE   BRAIN    CENTERS 

?      }  12 


AND   THE   OCULAR    MUSCLES. 
Z         1  1         ? 


101 


102  THE   BRAIN    CENTERS 

must  be  aided  by  the  fusion  faculty  of  the  mind,  which 
calls  into  action  the  right  and  left  fourth  basal  centers. 

What  is  the  source  of  trouble  in  esophoria?  Certainly 
not  the  conjugate  centers  controlling  the  externi  and  the 
interni,  for  these  centers  do  precisely  the  same  work  in 
esophoria  as  in  orthophoria.  If  they  develop  no  symp- 
toms in  the  latter  condition,  they  can  cause  none  in  the 
former.  There  are  but  two  kinds  of  brain  centers  con- 
nected with  the  lateral  recti,  and  since  one  class,  the  con- 
jugate centers,  cannot  cause  symptoms,  in  esophoria,  or 
in  any  other  form  of  heterophoria,  then  the  centers  belong- 
ing to  the  other  class,  the  basal  centers,  must  be  chargeable. 
The  basal  centers  of  the  interni,  the  right  and  left  third 
centers,  are  never  active  in  esophoria;  but  one  or  both  of 
the  right  and  left  fourth  basal  centers  must  be  in  a  con- 
stant state  of  activity  in  every  case  of  esophoria,  through- 
out every  waking  hour,  and  the  externus  connected  with 
an  active  fourth  basal  center  must  be  in  a  constant  state 
of  contraction.  The  basal  center  discharges  neuricity,  and 
the  weak  muscle  contracts  under  this  stimulus,  in  the  in- 
terest of  fusion — of  binocular  single  vision.  The  excited 
basal  centers,  right  and  left  fourth,  and  the  contracting 
external  recti  muscles,  one  or  both,  develop  all  the  symp- 
toms that  present  themselves  in  esophoria. 

Treatment  of  Esophoiia. — All  treatment  should  aim  at 
bringing  about  such  a  condition  of  the  lateral  recti  muscles 


AND    THE   OCULAR    MUSCLES.  103 

and  the  brain  centers  connected  with  them  as  will  enable 
the  third,  fourth  and  fifth  conjugate  centers,  under  the  in- 
fluence of  volition,  to  perfectly  control  the  external  and 
internal  recti,  unaided  by  the  right  and  left  fourth  basal 
centers,  whose  normal  state  is  restfulness.  This  can  be 
done  in  one  of  three  way:  First,  a  prism  before  each  eye, 
the  strength  equally  divided,  and  the  base  of  each  out,  the 
two  completely  correcting  the  esophoria,  would  allow  both 
eyes  to  assume  positions  that  would  make  the  tonicity  of 
the  weak  externus  balance  the  tonicity  of  the  strong  inter- 
nus,  without  diplopia.  These  prisms  would  relieve  the 
right  and  left  fourth  basal  centers  of  any  necessity  for  ac- 
tion— would  place  them  at  rest,  in  direct  distant  vision,  and 
in  convergence,  but  not  in  versions.  But  there  are  two  ob- 
jections to  prisms  for  esophoria,  especially  to  strong  prisms: 
one  is  that  they  always  interfere  with  the  law  of  direc- 
tion; the  other  is  that  unless  the  interni  are  ideally  at- 
tached to  the  sclera,  either  a  plus  or  minus  cyclophoria 
would  be  caused  by  the  prisms.  The  first  of  these  objec- 
tions always  exists,  and  the  second  is  not  uncommon,  and 
is  always  serious. 

The  second  plan  of  treatment  is  to  develop  the  weak  ex- 
terni,  by  means  of  rhythmic  exercise,  so  as  to  make  their 
tonicity  equal  the  tonicity  of  the  interni.  This  would  cer- 
tainly and  effectively  relieve  the  right  and  left  fourth  basal 
centers  of  any  demand  for  activity — would  place  them  at 


104  THE   BRAIN    CENTERS 

rest.  Patience  and  perseverance  are  the  essential  factors 
in  carrying  out  this  plan  of  treatment. 

The  third  plan  of  treating  esophoria  is  to  give  equal 
tonicity  by  operations.  This  is  the  quickest,  and,  if  the 
error  be  great,  it  is  the  best  method.  This  result  can  be 
accomplished  by  weakening  the  two  interni  by  partial 
tenotomies,  or  by  strengthening  the  two  externi  by  short- 
ening or  advancement.  In  the  higher  degrees  of  esophoria, 
tenotomies  of  both  interni  and  shortenings  of  both  externi 
must  be  done  in  order  to  relieve  the  two  fourth  basal  cen- 
ters. In  doing  these  operations,  the  aim  should  be  rather 
to  fall  short  of  a  full  correction  than  convert  an  esophoria 
into  an  exophoria. 

All  emmetropes,  regardless  of  age,  who  have  esophoria, 
may  be  benefitted  by  wearing  convex  lenses  for  all  near 
work.  These  lenses  lessen  the  demand  on  the  tenth  con- 
jugate center,  and  correspondingly  lessen  the  activity  of 
the  third  conjugate  center.  The  smaller  quantity  of  neu- 
ricity  sent  to  the  interni  excites  a  slighter  contraction  of 
these  muscles,  and  thus  the  esophoria  in  the  near  is  lessened 
if  not  relieved.  About  2°  of  esophoria  in  the  near  is  re- 
lieved by  a  +1  D.  lens.  Convex  lenses  should  be  given,  for 
near  work,  to  young  emmetropes  who  are  esophoric,  only 
when  prisms,  exercise  and  operations  are  declined.  Con- 
vex lenses  would  not  alter  the  esophoria  of  emmetropes,  in 
distant  seeing. 


AND   THE   OCULAR    MUSCLES.  105 

Exophoria. — Plate  XXI.  represents  a  pair  of  emmetropic- 
exophoric  eyes  and  the  brain  centers  that  must  control  them 
in  straight-forward  distant  vision.  The  head  is  in  the  pri- 
mary position,  and  the  point  to  be  fixed  is  at  practical  in- 
finity and  in  the  line  of  intersection  of  the  extended  median 
and  horizontal  planes  of  the  head.  The  externi,  having 
greater  tonicity  than  the  interni,  would  cause  the  visual 
axes  to  diverge,  and  the  point  of  view  would  be  doubled. 
To  prevent  this  the  fusion  faculty  of  the  mind  causes  the 
right  and  left  third  basal  centers  to  send  neuricity  to  their 
respective  interni,  that  their  tonicity  may  be  supplemented 
by  enough  contractility  to  prevent  the  divergence  of  the 
visual  axes.  Contrasting  Plate  VII.  with  this  plate,  it  will 
be  seen  that,  in  the  former,  all  brain  centers  are  at  rest, 
and  that  no  muscle  is  active,  while  in  the  latter  the  right 
and  left  third  basal  centers  are  discharging  neuricity  con- 
tinuously to  the  weak  interni,  and  that  these  muscles  are 
just  as  continuously  in  a  state  of  contraction.  All  other 
centers  and  muscles  are  just  as  restful  in  Plate  XXI.  as 
in  Plate  VII.  Exophoric  eyes  that  are  emmetropic  give 
trouble,  in  distant  vision,  only  because  of  the  work  of  the 
right  and  left  third  basal  centers  and  the  consequent  con- 
traction of  the  interni. 

Plate  XXII.  represents  the  same  pair  of  eyes  in  the  act 
of  accommodating  and  converging.     A  comparison  of  Plate 


106 


THE   BRAIN   CENTERS 


AND    THE    OCULAR    MUSCLES. 


107 


HAZEXXZ 


108 


THE   BRAIN   CENTERS 
2        1  12 


AND   THE   OCULAR    MUSCLES. 

?     i  )      2 


109 


110  THE   BRAIN   CENTERS 

VIII.  with  this  Plate :  the  only  difference  shown  is  that,  in 
the  latter,  lines  have  been  drawn  from  the  right  and  left 
third  basal  centers  to  the  interni  to  show  that  both  the 
centers  and  the  muscles  are  active.  The  work  being  done 
by  the  third  and  tenth  conjugate  centers  in  Plate  XXII.  is 
precisely  the  same  that  is  being  done  by  these  centers  in 
Plate  VIII.  The  symptoms  caused  by  the  use  of  emme- 
tropic-exophoric  eyes  in  near  work  must  be  chargeable 
against  the  corrective  activity  of  the  right  and  left  third 
basal  centers  and  the  added  contractility  of  the  two  interni. 

Plate  XXIII.  represents  the  same  eyes  in  the  act  of  right 
version.  The  fourth  conjugate  center  that  effects  right 
version,  in  perfect  harmony,  in  Plate  IX.,  cannot  do  so 
in  Plate  XXIII.,  for  the  reason  that  the  tonicity  of  the  right 
externus  is  greater  than  that  of  the  left  internus.  That 
the  left  eye  may  rotate  to  the  right  in  harmony  with  the 
fellow  eye,  its  weak  internus  must  receive  supplemental  neu- 
ricity  from  the  left  third  basal  center.  In  the  right  rota- 
tion of  esophoric  eyes  the  fourth  conjugate  center  does  pre- 
cisely the  same  work  that  it  performs  in  effecting  the  same 
rotation  of  orthophoric  eyes,  hence  it  cannot  cause  symp- 
toms in  the  former  and  not  cause  them  in  the  latter. 
Symptoms  therefore,  must  be  caused  by  the  excited  left 
third  basal  center  and  the  consequent  extra  contraction  of 
the  left  internus. 

Plate  XXIV.  represents  the  same  eyes  in  the  act  of  left 


AND  THE  OCULAR  MUSCLES.  Ill 

version.  The  left  externus  having  greater  tonicity  than  the 
right  internus,  it  would  be  impossible  for  the  fifth  conju- 
gate center  to  effect  harmonious  left  version.  To  prevent 
diplopia,  the  right  third  basal  center  must  send  supple- 
mental neuricity  to  the  weak  right  internus.  Plate  X.  rep- 
resents the  normal  conditions  in  left  version.  The  dif- 
ference between  Plates  X.  and  XXIV.  must  be  the  abnor- 
mality shown  in  the  latter.  This  difference  is  activity  of 
the  right  third  basal  center  and  the  added  contractility  of 
the  right  internus.  Cure  the  exophoria  by  either  exercise 
of  both  interni  or  by  partial  tenotomy  of  both  externi  or 
by  shortening  both  interni,  then  the  right  third  basal  cen- 
ter will  not  become  active  in  left  version  of  the  eyes,  the 
only  active  center  being  the  fifth  conjugate.  Concave 
lenses  for  both  distant  and  near  vision  would  relieve  the 
two  third  basal  centers  by  exciting  the  third  conjugate  cen- 
ter. 

Hyperphoria  and  Cataphoria. — Plate  XXV.  represents  a 
pair  of  eyes,  the  left  being  hyperphoric  and  the  right  cata- 
phoric, the  gaze  being  straight-forward  and  the  point  of 
fixation  in  the  line  of  intersection  of  the  extended  median 
and  horizontal  planes  of  the  head,  at  practical  infinity.  No 
conjugate  center  is  excited;  but,  to  keep  the  visual  axes 
in  the  extended  horizontal  plane,  the  right  first  basal  center 
must  send  neuricity  to  the  weak  right  superior  rectus,  and 
the  left  second  basal  center  must  send  neuricity  to  the  weak 


112 


THE   BRAIN   CENTERS 

3    1  12 


AND   THE   OCULAR    MUSCLES.  113 

left  inferior  rectus.  Otherwise  there  would  be  diplopia. 
Correct  this  error  by  either  exercise  or  operations,  then 
these  two  basal  centers  would  lapse  into  their  normal  state 
of  rest.  The  result — restful  state  of  both  muscles  and  brain 
centers — would  be  represented  by  Plate  VII. 

Plate  XXVI.  represents  the  upward  version  of  the  same 
pair  of  eyes.  The  first  conjugate  center  sends  an  equal 
amount  of  neuricity  to  both  superior  recti,  but  with  unequal 
results.  The  tonicity  of  the  left  superior  rectus  being 
greater  than  that  of  the  right  superior  rectus,  the  right 
eye  would  not  rotate  as  fast  as  the  left  unless  supplemental 
neuricity  should  be  sent  by  the  right  first  basal  center  to 
the  weak  right  superior  rectus.  In  upward  version  the  sev- 
enth conjugate  center  is  active  to  prevent  inward  torsion- 
ing  of  the  eyes.  The  abnormal  work  done  by  both  brain 
and  muscle  in  the  upward  rotation  is  shown  by  contrasting 
Plate  XXVI.  with  Plate  XI,  the  latter  showing  the  upward 
rotation  of  orthophoric  eyes.  This  abnormality  consists 
of  activity  of  the  right  first  basal  center  and  the  excessive 
contraction  of  the  right  superior  rectus.  If  the  first  and 
seventh  cortical  centers  cause  no  symptoms  in  the  upward 
rotation  of  orthophoric  eyes,  these  centers,  doing  precisely 
the  same  work  in  superverting  hyperphoric  and  cataphoric 
eyes,  as  shown  in  Plate  XXVI.,  can  cause  no  symptoms. 
The  discomfort,  therefore,  must  come  from  excitation  of 
the  right  first  basal  center  and  the  resulting  excessive  con- 


114 


THE   BRAIN   CENTERS 

2 


AND   THE   OCULAR    MUSCLES. 


115 


116  THE   BRAIN   CENTERS 

traction  of  the  right  superior  rectus.  Giving  equal  tonic- 
ity to  the  superior  and  inferior  recti  by  either  exercise  or 
operations,  allows  the  right  first  basal  center  to  remain  in- 
active in  the  upward  rotation,  hence  there  could  be  no 
symptoms. 

Plate  XXVII.  represents  the  downward  rotation  of  the 
same  pair  of  eyes.  The  abnormal  action  in  this  plate  can 
be  easily  seen  by  contrasting  it  with  Plate  XII.,  which  rep- 
resents the  active  brain  centers  and  contracting  muscles 
in  the  subversion  of  orthophoric  eyes.  In  the  downward 
version  shown  in  Plate  XXVII.  the  left  inferior  rectus  must 
receive  supplemental  neuricity  from  the  left  second  basal 
center,  or  there  would  be  diplopia.  The  second  and  sixth 
conjugate  centers  act  on  hyperphoric  eyes  as  they  act  on 
orthophoric  eyes,  hence  they  do  not  excite  symptoms  of  any 
character.  Equalizing  the  tonicity  of  the  superior  and  infe- 
rior recti  of  the  eyes  shown  in  Plate  XXVII.  converts  this 
plate  into  Plate  XII. 

Plus  and  Minus  Cyclophoria. — Plate  XXVIII.  represents 
a  pair  of  eyes  having  plus  cyclophoria.  The  head  is  in  the 
primary  position,  and  the  eyes  are  also  in  their  primary 
positions.  The  recti  muscles  are  all  normal  in  tonicity, 
hence,  without  brain  excitement,  the  visual  axes  lie  in  the 
extended  horizontal  plane  and  are  practically  parallel  with 
each  other.  The  inferior  obliques  having  greater  tonicity 
than  the  superior  obliques,  would  cause  both  vertical  axes 


AND   THE   OCULAR    MUSCLES.  117 

to  deviate  from  the  median  plane  of  the  head,  and  there 
would  be  diplopia.  If  the  error  is  equal  in  the  two  eyes, 
the  sixth  conjugate  center  acting  alone  can  prevent  the 
diplopia  by  sending  an  equal  quantity  of  neuricity  to  the 
weak  superior  obliques.  This  is  shown  'in  the  plate.  If 
the  right  superior  oblique  should  be  weaker  than  the  left, 
the  right  sixth  basal  center  would  have  to  send  supple- 
mental neuricity  to  this  weaker  muscle  in  order  that  the 
two  might  act  in  harmony.  The  sixth  cortical  center  and 
the  right  and  left  sixth  basal  centers  are  all  under  the  con- 
trol of  the  fusion  faculty  of  the  mind.  Correcting  the  plus 
cyclophoria  by  exercising  the  superior  obliques  transforms 
Plate  XXVIII.  into  Plate  VII,  and  all  symptoms  must  dis- 
appear. Relief  will  also  attend  the  placing  of  either  plus 
or  minus  cylinders,  given  for  the  correction  of  astigma- 
tism, in  positions  of  rest  for  the  weak  superior  obliques. 

It  is  not  improbable  that  plus  cyclophoria  is  entirely  cor- 
rected by  activity  of  the  right  and  left  sixth  basal  centers, 
and,  if  so,  Plate  XXXVI.  should  be  substituted  for  Plate 
XXVIII. 

Plus  cyclophoria  is  corrected  in  superversion  by  the  ac- 
tion of  the  first  conjugate  center  on  the  superior  recti,  for 
these  muscles  in  raising  the  eyes  would  counteract  the  ten- 
dency towards  outward  torsion,  thus  relieving  the  sixth 
conjugate  center,  or  the  right  and  left  sixth  basal  centers, 
and  the  superior  obliques.     The  seventh  conjugate  center 


118 


THE   BRAIN   CENTERS 


I      2 


AND   THE   OCULAR    MUSCLES. 


119 


120  THE   BRAIN   CENTERS 

and  the  inferior  obliques  take  a  smaller  part  in  superver- 
sion  when  there  is  plus  cyclophoria  than  when  there  is 
orthophoria  of  the  obliques. 

Plate  XXIX.  shows  the  centers  and  muscles  concerned  in 
subversion  of  eyes  that  have  plus  cyclophoria.  The  second 
cortical  center  acting  on  the  inferior  recti  would  rotate 
the  eyes  down  and  produce  an  excessive  plus  torsioning  be- 
cause of  the  already  existing  plus  cyclophoria.  It  may  be 
supposed  that  the  sixth  cortical  center  would  so  act  on  the 
weak  superior  obliques  as  to  help  the  inferior  recti  depress 
the  eyes  and  correct  the  torsioning  error  of  the  latter,  leav- 
ing the  correction  of  the  plus  cyclophoria  to  the  right  and 
left  sixth  basal  centers.  Thus  it  is  shown  that  weak  superior 
obliques  have  to  do  excessive  work  whenever  the  point  of 
fixation  is  below  the  horizontal  plane,  and  that  the  extra 
neuricity  demanded  comes  from  the  right  and  left  sixth 
basal  centers  that  ought  to  be  at  rest.  Correction  of  the 
plus  cyclophoria  by  exercising  the  superior  obliques,  or  by 
properly  shifting  the  axes  of  plus  or  minus  cylinders  given 
for  the  correction  of  astigmatism,  relieves  these  basal  cen- 
ters in  reading  or  other  near  work.  The  only  additional 
means  of  relief  to  the  centers  and  to  the  weak  superior 
obliques  is  in  depressing  the  head  so  that  the  extended  fixed 
horizontal  plane  of  the  head  may  fall  below  the  plane  of 
the  visual  axes.  A  person  with  uncomplicated  plus  cyclo- 
phoria habitually  carries  his  head  with  his  face  cast  down, 


AND   THE   OCULAR   MUSCLES.  121 

as  also  does  the  one  with  double  hyperphoria.  Such  a 
person  should  be  treated  for  his  physical  defect  and  not 
condemned  because  of  a  supposed  mental  obliquity.  The 
relief  of  the  plus  cyclophoria  transforms  Plate  XXIX.  into 
Plate  XII.,  the  latter  illustrating  the  downward  sweep  of 
orthophoric  eyes. 

Plate  XXX.  represents  a  pair  of  minus  cyclophoric  eyes, 
both  the  head  and  the  eyes  being  in  their  primary  positions, 
the  point  of  fixation  in  the  line  of  intersection  of  the  ex- 
tended median  and  horizontal  fixed  plane  of  the  head  and 
at  practical  infinity.  All  of  the  recti  muscles  and  the  two 
superior  obliques  are  in  a  state  of  tonicity,  and  the  cortical 
and  basal  centers  connected  with  them  are  at  rest;  but  to 
maintain  parallelism  between  the  vertical  axes  of  the  eyes 
and  the  median  plane  of  the  head,  the  seventh  conjugate 
center  or  the  right  and  left  seventh  basal  centers  must  send 
neuricity  to  the  weak  inferior  obliques  so  that  contractility 
may  supplement  tonicity,  thus  enabling  them  to  perfectly 
balance  the  stronger  superior  obliques.  A  cure  of  the 
minus  cyclophoria  by  exercise,  or  correcting  it  by  properly 
shifting  plus  or  minus  cylinders,  converts  Plate  XXX.  into 
Plate  VII.  The  upward  gaze  of  minus  cyclophoric  eyes 
makes  excessive  demands  on  the  inferior  obliques,  and  the 
seventh  conjugate  and  right  and  left  seventh  basal  centers 
controlling  them.  Minus  cyclophoria  is  probably  entirely 
corrected  by  activity  of  the  right  and  left  seventh  basal  cen- 


122 


THE   BRAIN   CENTERS 

2 


FLA  IE XXX 


AND   THE   OCULAR    MUSCLES. 


123 


2        1 


\  ? 


124  THE   BRAIN   CENTERS 

ters,  and,  if  so,  Plate  XXXVII.  should  be  substituted  for 
Plate  XXX. 

Plate  XXXI.  shows  that  when  the  point  of  view  is  below 
the  extended  horizontal  plane  of  the  head,  the  brain  centers 
and  muscles  have  less  to  do,  if  there  is  minus  cyclophoria, 
than  when  there  is  orthophoria.  This  can  be  seen  at  a 
glance  by  contrasting  Plate  XXXI.  with  Plate  XII.  In 
Plate  XXXI.  the  outward  torsioning  effect  of  the  inferior 
recti  only  counteracts  the  minus  cyclophoria.  There  is  no 
need  for  excitation  of  the  sixth  conjugate  center,  because 
the  tonicity  of  the  strong  superior  obliques  will  prevent  an 
outward  torsioning  by  the  inferior  recti  under  the  influence 
of  the  second  conjugate  center.  The  person  who  has  un- 
complicated minus  cyclophoria,  like  the  one  who  has  double 
cataphoria,  carries  a  high  head,  usually  erroneously  thought 
to  be  indicative  of  a  proud  spirit. 

Up  to  this  point  the  several  heterophoric  conditions  have 
been  studied  as  if  only  a  single  one  existed  in  any  given 
case.  The  truth  is,  that  two  or  more  of  these  errors  very 
often  co-exist,  thus  complicating  the  case  both  as  to  the 
number  of  basal  centers  that  must  be  active,  and  the  num- 
ber of  muscles  that  must  be  continually  in  a  state  of  con- 
traction. Combined  errors  are  more  likely  to  cause  symp- 
toms than  is  a  single  error. 

A  combination  of  Plates  XVII.  and  XXV.  will  show  that, 
in  hyper-esophoria,  four  basal  centers  must  be  continually 


AND   THE   OCULAR    MUSCLES.  125 

discharging  neuricity  to  their  respective  muscles,  that  diplo- 
pia may  be  prevented.  A  combination  of  Plates  XVII. ,  XXV. 
and  XXVIII.  will  show  that,  in  hyper-esophoria  compli- 
cated with  plus  cyclophoria,  six  basal  centers  and  their  six 
muscles  must  be  active  in  the  interest  of  binocular  single 
vision.  In  all  these  plates  the  eyes  represented  are  in  their 
primary  positions  and  the  head  is  erect.  The  restfulness 
of  brain  centers  and  muscles  of  orthophoric  eyes,  the  head 
and  eyes  being  in  their  primary  positions,  is  shown  in  Plate 
VII.  Orthophoria  is  harmless  for  the  reason  that  no  basal 
center  is  ever  awakened  from  its  normal  state  of  restful- 
ness ;  all  heterophoric  conditions  are  harmful  for  the  reason 
that  one  or  several  basal  centers  and  their  respective  mus- 
cles must  be  continually  active  for  the  prevention  of  di- 
plopia, throughout  all  the  waking  hours  of  every  day  of 
one's  life.  Withdrawal  from  near  work  brings  rest  to 
orthophoric  eyes  and  to  the  conjugate  centers  connected 
with  them;  there  is  no  rest  for  heterophoric  eyes  nor  for 
the  basal  centers  connected  with  the  weaker  muscles,  ex- 
cept in  sleep. 

In  right  version  of  hyper-esophoric  eyes  three  basal  cen- 
ters,, the  right  fourth,  the  right  first  and  the  left  second,  will 
be  actively  combating  diplopia.  This  can  be  seen  by  com- 
bining Plates  XIX.  and  XXV.,  for  the  latter  plate  repre- 
sents the  action  of  the  right  first  and  left  second  basal 
centers  not  only  in  the  straight-forward  gaze,  but  also  in 


126  THE   BRAIN    CENTERS 

both  right  and  left  version  as  well.  One  conjugate  center, 
the  fourth,  is  alone  concerned  in  the  right  version  of  ortho- 
phoric  eyes,  as  shown  in  Plate  IX. ;  but,  as  shown  above,  the 
right  sweep  of  hyper-esophoric  eyes  is  effected  by  activity 
of  the  same  conjugate  center,  the  fourth,  but  there  is  also 
associated  activity  of  three  basal  centers. 

In  the  straight-forward  gaze  of  hyper-eso-plus-cyclophor- 
ic  eyes  (the  left  eye  being  hyperphoric) ,  four,  if  not  six, 
basal  centers  are  active,  the  right  and  left  fourth,  the  right 
first  and  left  second,  and  probably  the  right  and  left  sixth, 
although  the  sixth  conjugate  center  could  do  the  work  of 
keeping  the  vertical  axes  of  the  eyes  parallel  with  the 
median  plane  of  the  head.  These  excited  centers  can  be 
seen  by  a  mental  combination  of  Plates  XVII.,  XXV.  and 
XXVIII.  The  restfulness  of  muscles  and  brain  centers  in 
direct  vision  when  there  is  orthophoria,  can  be  appreciated 
to  the  fullest  by  now  glancing  at  Plate  VII.  To  relieve  the 
basal  centers  in  any  form  or  heterophoria  or  in  any  com- 
bination of  heterophoric  conditions,  the  relationship  of  the 
recti  muscles  must  be  readjusted  either  by  operations,  by 
exercise  or  by  prisms  in  positions  of  rest;  and  that  of  the 
obliques  must  be  readjusted  by  means  of  cylinders  for  either 
exercise  or  rest,  or  by  so  operating  on  a  rectus  muscls  as 
to  relieve  the  cyclophoria. 

Not  more  than  three  conjugate  centers  are  ever  active 
in  effecting  ocular  rotations,  whether  the  eyes  are  ortho- 


AND   THE   OCULAR    MUSCLES.  127 

phoric  or  heterophoric.  All  possible  rotations  of  ortho- 
phoria eyes  are  accomplished  without  excitation  of  a  single 
basal  center.  Heterophoric  eyes  can  assume  no  position 
and  maintain  binocular  single  vision,  without  excitation  of 
from  one  to  six  basal  centers.  The  exact  basal  centers  dis- 
turbed in  any  given  rotation  of  simple  or  complicated 
heterophoric  eyes  may  be  easily  determined.  For  every  dis- 
turbed basal  center  there  is  abnormal  contraction  of  an 
ocular  muscle.  If  six  basal  centers  are  simultaneously  dis- 
turbed, six  muscles  are  made  to  respond  for  the  prevention 
of  diplopia. 

It  is  -an  interesting  fact  to  note  that,  in  cases  of  hetero- 
phoria,  fewer  basal  centers  are  excited  when  the  point  of 
view  is  secondary  than  when  the  eyes  and  head  are  in  their 
primary  positions.  This  is  shown  in  Plates  XVIL,  XIX. 
and  XX.,  illustrating  three  positions  of  esophoric  eyes. 
To  determine  that  the  same  thing  is  true  of  exophoric  eyes, 
one  need  only  examine  Plates  XXL,  XXIII.  and  XXIV. 
This  truth  is  also  made  clear  as  to  hyper-cataphoria  by 
examination  of  Plates  XXV.,  XXVI.  and  XXVII.  It  is 
further  remarkable  that,  while  the  primary  position  of 
heterophoric  eyes  disturbs  the  largest  number  of  basal  cen- 
ters, the  same  position  allows  all  conjugate  centers  to  lapse 
into  a  state  of  repose.  Since  in  orthophoria  eyes  no  basal 
center  is  ever  excited,  it  must  appear  that  in  the  primary 
positions  of  such  eyes  there  is  absolute  restf illness  of  all 


128  THE   BRAIN   CENTERS 

conjugate  and  basal  centers,  and  consequent  inaction  of  all 
the  ocular  muscles.  This  is  shown  in  Plate  VIL,  already 
frequently  referred  to. 

The  muscle  errors  so  far  studied  may  be  classed  as  true 
heterophoric  conditions,  in  contrast  with  other  errors  to  be 
studied  later  under  the  name  of  pseudo-heterophoria.  The 
cause  of  every  form  of  true  heterophoria  is  muscular.  It 
must  appear,  therefore,  to  every  careful  student  that  the 
treatment  of  every  form  of  true  heterophoria  must  be  di- 
rected to  the  muscles.  Whatever  the  method  of  treatment 
may  be,  the  aim  should  be  to  equalize  the  tonicity  of  op- 
posing muscles,  so  that  the  basal  brain  centers  may  lapse 
into  that  state  of  rest  which  is  normal  to  them  when  eyes 
are  orthophoric.  To  determine  what  plan  of  treatment 
shall  be  adopted  in  any  given  case,  the  surgeon  should  re- 
sort to  the  tonicity,  version  and  duction  tests,  as  set  forth 
in  the  first  chapter  of  this  book.  Rhythmic  exercise  of 
the  weaker  muscles  will  accomplish  this  purpose,  in  suit- 
able cases,  by  increasing  their  tonicity;  in  other  cases, 
shortening  or  tucking  the  weaker  muscles  will  increase 
their  tonicity  up  to  the  point  desired;  in  still  other  cases 
partial  tenotomies  of  the  stronger  muscles  will  lessen  their 
tonicity,  so  that  they  may  perfectly  balance  the  tonicity  of 
their  antagonists.  Since  the  author  intends  this  little  book 
only  as  a  companion  volume  to  his  other  book,  Ophthalmic 
Myology,  the  reader  is  referred  to  the  latter  for  an  ex- 


AND   THE   OCULAR    MUSCLES.  129 

tended  and  trustworthy  study  of  methods  of  treatment.  A 
study  of  true  heterophoria  from  the  brain  side  of  the  ques- 
tion has  but  emphasized  the  teaching  in  Ophthalmic  Myol- 
ogy, that  all  treatment  must  be  directed  to  the  muscles. 

A  fitting  conclusion  to  this  chapter  will  be  a  study  of 
multiple  errors  that  may  be  caused  by  one  muscle,  and  how 
to  treat  such  a  muscle.  If  a  too  strong  internus  is  attached 
too  high,  the  error  causes  both  a  hyperphoria  and  a  minus 
cyclophoria,  as  well  as  esophoria.  If  it  is  attached  too  low, 
this  error  causes  both  a  cataphoria  and  a  plus  cyclophoria, 
as  well  as  esophoria.  If  a  too  strong  externus  is  attached  too 
low,  this  error  will  cause  a  cataphoria  and  a  minus  cyclo- 
phoria, as  well  as  exophoria.  If  attached  too  high,  this 
error  will  cause  a  hyperphoria  and  a  plus  cyclophoria,  as 
well  as  exophoria.  A  too  strong  superior  rectus  attached  too 
far  nasal-ward  will  cause  esophoria  and  plus  cyclophoria,  as 
well  as  hyperphoria.  A  too  strong  inferior  rectus  attached 
too  far  nasal-ward  will  cause  an  esophoria  and  a  minus 
cyclophoria,  as  well  as  cataphoria;  but  if  attached  too  far 
temple-ward  it  will  cause  an  'exophoria  and  a  plus  cyclo- 
phoria, as  well  as  cataphoria.  A  knowledge  of  the  hetero- 
phorias  affecting  the  superior  and  inferior  recti  and  the  two 
obliques  is  of  supreme  importance  in  connection  with  op- 
erative work  on  the  lateral  recti  muscles,  for  the  cure  of  in- 
trinsic heterophorias  affecting  them.  How  to  operate  with 
the  view  of  altering  the  tension  of  a  rectus  muscle,  with  or 


130  THE   BRAIN   CENTERS 

without  changing  its  plane  of  rotation,  is  fully  set  forth  in 
Ophthalmic  Myology,  to  which  the  reader  is  again  referred. 
To  do  a  tenotomy  on  a  lateral  rectus  muscle,  or  to  shorten 
or  advance  it,  without  knowing  whether  or  not  its  plane  of 
rotation  should  be  changed,  is  to  err,  which  may  be  human, 
but  certainly  is  not  scientific.  To  fail  to  change  the  plane 
in  making  a  tenotomy  of  an  internus  when  there  is  a  plus 
cyclophoria,  whether  the  cause  is  in  the  obliques  or  in  faulty 
attachment  of  a  rectus  muscle,  is  to  leave  uncorrected  a 
most  important  error;  to  change  the  plane  of  an  internus 
when  there  is  no  cyclophoria  is  to  bring  into  existence  a 
cyclophoria  which  will  ever  be  a  source  of  trouble.  To  de- 
termine the  character  of  operation  to  be  done  on  a  rectus 
muscle  may  appear  to  be  a  difficult  problem,  but  in  reality  it 
is  easy  of  solution.  The  tonicity  and  duction  tests  of  all  the 
recti,  and  the  tonicity  test  of  the  obliques,  determine  in  every 
case  whether  the  tonicity  of  the  stronger  rectus  should  be 
lessened  by  a  partial  tenotomy,  or  that  the  tonicity  of  its 
weak  antagonist  should  be  increased  by  a  shortening  or  ad- 
vancement; and  these  tests  also  determine  whether  or  not 
the  muscle  plane  should  be  changed. 

Whence  come  the  symptoms  of  heterophoria  is  a  question 
that  may  never  be  satisfactorily  answered.  Do  they  come 
directly  from  activity  of  basal  brain  centers  whose  normal 
state  is  rest?  Or  do  they  come  from  the  fusional  contrac- 
tion of  the  ocular  muscles?     There  must  be  the  two  co-ex- 


AND   THE   OCULAR    MUSCLES.  131 

isting  states :  brain  center  excitation  and  muscle  contrac- 
tion. May  not  the  forced  activity  of  the  fusion  faculty  of 
the  mind  for  the  time  suspend,  or  otherwise  interfere  with, 
some  other  faculty  of  the  mind — just  as  deep  thinking  may 
modify  the  faculty  of  hearing,  or  just  as  the  mastery  of  an 
emotion  may  suspend  the  power  of  reasoning?  Intense 
and  unceasing  activity  of  any  one  mental  faculty  must 
cripple,  to  a  greater  or  less  extent,  every  other  mental  fac- 
ulty. Some  faculty  of  the  mind  must  preside  over  every 
organ  of  the  body.  It  must  appear  that  each  of  these  fac- 
ulties can  do  its  best  only  when  no  other  faculty  is  over- 
taxed. The  fusion  power  is  a  mental  faculty  that  presides 
over  a  little  kingdom  at  the  base  of  the  brain,  consisting 
of  twelve  individual  centers,  each  of  these  centers  being 
connected  with  a  single  ocular  muscle.  This  mental  power, 
as  already  shown,  has  nothing  to  do  when  the  two  eyes 
are  orthophoria  hence  could  not  be  a  source  of  interference 
with  any  other  mental  process.  In  heterophoria  the  fusion 
faculty  must  be  continually  active  during  all  waking  hours, 
hence  may  impair  the  effective  working  of  any  or  all  other 
faculties.  Since  correcting  heterophoric  conditions  brings 
rest  to  the  fusion  faculty  of  the  mind  as  well  as  to  the  basal 
centers  and  their  respective  muscles,  such  work  should  not 
be  neglected. 

Symptoms  may  arise  from  overwork  of  the  weak  ocular 
muscles,  because  of  a  ptomaine  or,  more  correctly  speaking, 


132  THE   BRAIN   CENTERS 

a  leucomaine,  generated  by  their  unremitting  contraction. 
This  substance,  by  its  action  on  the  sensory  nerve  endings 
in  the  muscles,  may  disturb  the  sensory  area  of  the  cortex, 
and  thus  excite  the  sensory  symptoms  of  which  such  pa- 
tients complain.  It  would  hardly  account  for  disturbance  of 
secreting  and  excreting  organs,  for  confusion  of  thought, 
and  for  convulsion  seizures.  But  from  whatever  stand- 
point we  may  view  the  symptomatology  of  heterophoria, 
there  can  be  but  one  logical  conclusion  as  to  treatment — 
that  is,  to  readjust  the  relationship  between  the  muscles, 
so  that  there  may  be  equality  of  tonicity.  From  this  read- 
justment by  exercise  or  operations  comes  rest  to  the  fusion 
faculty  of  the  mind,  rest  to  the  basal  centers,  and  rest  to 
the  muscles.  Relief  cannot  come  through  the  mind,  nor  as 
a  result  of  any  attempt,  however  impossible,  to  change  the 
nature  of  the  basal  centers,  so  that  work  to  them  may  be 
the  same  as  rest.  So  long  as  there  is  unequal  tonicity  of 
the  ocular  muscles,  binocular  single  vision  will  be  possible 
only  as  the  result  of  disturbed  mental  equilibrium,  over- 
worked brain  centers,  and  unceasing  muscle  contraction. 

From  the  standpoint  of  basal  centers,  none  of  the  several 
kinds  of  heterophoria  involving  the  recti  muscles  can  exist 
in  monocular  vision,  notwithstanding  the  fact  that  opposing 
muscles  may  be  unequal  in  tonicity.  Cyclophoria  alone  is 
a  condition  that  is  as  important  when  there  is  only  one  eye 
as  when  there  are  two,  for  the  vertical  axis  must  be  kept 


AND    THE   OCULAR    MUSCLES.  133 

parallel  with  the  median  plane  of  the  head  in  both  monocu- 
lar and  binocular  vision,  that  there  may  be  correct  orienta- 
tion. No  basal  center  connected  with  a  rectus  muscle  is 
ever  active  if  there  is  but  one  eye.  This  explains  the  fact 
that  many  persons  who  have  lost  one  eye  by  disease  or  ac- 
cident, the  condition  being  such  as  not  to  excite  sympathy, 
have  stronger  and  more  comfortable  vision  with  the  one 
eye  than  they  ever  had  with  the  two  eyes.  If  nothing 
could  be  done  for  equalizing  tonicity  of  the  ocular  muscles, 
to  many  individuals  the  loss  of  one  eye  would  not  be  a  mis- 
fortune. 

"Two  eyes  are  better  than  one"  only  when  the  muscles 
are  well  adjusted.  Readjustment  of  unbalanced  muscles 
is  one  of  the  great  achievements  of  modern  surgery. 


CHAPTER   III. 


AMETROPIA  AND  PSEUDO-HETEROPHORIA. 


Every  form  of  ametropia  has  associated  with  it  a  pseudo- 
heterophoria,  and  they  are  related  to  each  other  as  cause  and 
effect.  There  is  no  pseudo-hyperphoria  or  cataphoria,  nor 
is  a  pseudo-cyclophoria  possible  as  a  result  of  ametropia. 

From  what  has  been  said  above,  it  would  appear  that 
errors  of  refraction  can  affect,  through  the  nerve  centers, 
only  the  lateral  recti  muscles,  and  this  is  true.  Pseudo-eso- 
phoria  or  pseudo-exophoria,  one  or  the  other,  exists  in  con- 
nection with,  and  is  caused  by,  every  error  of  refraction. 
The  higher  the  refractive  error,  the  greater  is  the  lateral 
pseudo-heterophoria.  Pseudo-exophoria  can  show  itself — 
can  exist — only  in  the  near.  Pseudo-esophoria  may  exist 
in  both  far  and  near  seeing. 

The  pseudo-errors  of  the  lateral  recti  muscles  may  exist 
alone  or  in  combination  with  either  intrinsic  esophoria  or 
intrinsic  exophoria.  If  there  is  pseudo-esophoria  it  may 
show  itself  as  an  esophoria  when  there  is  lateral  orthopho- 
ria, or  it  may  increase  an  existing  intrinsic  esophoria.,  or 
it  may  simply  lessen,  cancel  or  conceal  an  intrinsic  exopho- 

(134) 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  135 

ria.  In  the  first  and  second  instances  the  pseudo-esophoria 
is  a  bad  thing  and  should  be  cured  by  correcting  the  focal 
error  causing  it;  in  the  latter  instance  the  pseudo-esopho- 
phoria  is  a  blessing,  in  that  it  brings  some  relief  to  the  right 
and  left  third  basal  centers,  and,  for  that  reason,  the  focal 
error  causing  it  should  not  be  corrected. 

Remembering  that  pseudo-exophoria  exists  only  in  the 
near,  it  may  be  said  that  this  may  show  itself  as  exophoria 
when  there  is  true  orthophoria ;  it  may  show  itself  as  an  in- 
creased exophoria  because  of  an  existing  intrinsic  exo- 
phoria, or  it  may  in  part  or  wholly  neutralize  or  conceal  an 
intrinsic  esophoria.  In  the  first  and  second  instances,  the 
error  is  an  evil,  and  should  be  cured  by  a  correction  of  the 
focal  error  causing  it ;  but  in  the  third  instance  it  is  a  bless- 
ing, in  that  it  relieves  the  right  and  left  fourth  basal  cen- 
ters of  the  hard  task  they  otherwise  would  have  to  perform 
in  reading  or  other  near  work.  Thus  it  would  appear  that 
focal  errors  are  sometimes  a  blessing,  though  more  often 
they  constitute  an  evil. 

MYOPIA. 

Myopia  and  Orthophoria. — Plate  VII.  shows  the  brain 
rest  and  muscle  inaction  of  myopic-orthophoric  eyes,  when 
the  object  of  view  is  at  infinity,  and  in  line  of  intersection 
of  the  extended  median  and  horizontal  fixed  planes  of  the 
head.    Such  eyes,  so  far  as  distant  vision  is  concerned,  give 


136  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

the  same  rest  to  conjugate  and  fusion  brain  centers,  and 
the  muscles  under  their  control,  as  do  emmetropic-ortho- 
phoric  eyes,  the  only  difference  being  in  the  sharpness  of 
sight.  Sharpening  distant  vision,  by  giving  the  proper  con- 
cave lenses,  would  create  no  demand  for  activity  of  the  mus- 
cles or  the  brain  centers  controlling  them.  These  lenses 
would  make  the  eyes  emmetropic  and  leave  them  orthophor- 
ic  for  distance.  The  lenses  would  make  the  eyes  emmetropic 
for  near  work  and  would  also  make  them  orthophoric  in  the 
near,  by  relieving  the  pseudo-exophoria. 

Plate  XXXII.  shows  myopic-orthophoric  eyes  engaged  in 
near  work.  Supposing  the  myopia  to  be  3-D,  the  ciliary 
muscles  and  the  tenth  conjugate  center  would  be  at  rest 
when  the  point  of  view  is  at  thirteen  inches.  There  must 
be  convergence,  else  there  would  be  diplopia.  If  there  is  an 
unalterable  relationship  between  the  tenth  and  third  con- 
jugate centers,  the  latter  could  not  discharge  neuricity  for 
effecting  convergence,  while  the  tenth  center  remains  quiet. 
Nevertheless,  convergence,  by  means  of  activity  of  the  right 
and  left  third  basal  centers,  would  be  possible,  for  these 
centers  are  not  associated  in  action  with  the  tenth  conju- 
gate center.  If  the  basal  centers  (right  and  left  third)  con- 
verge myopic  eyes,  they  do  it  in  the  interest  of  binocular 
single  vision.  This  much  is  in  accord  with  the  supposition 
that  convergence  of  myopic-orthophoric  eyes  is  effected  by 
the  right  and  left  third  basal  centers:  if  myopic  eyes  are 


AMETROPIA  AND   PSEUDO-HETEROPHOrdA.  137 

orthophoric  in  the  distant  test,  they  always  show  exophoria 
in  the  near.  The  third  basal  centers  correct  an  exophoria 
whether  of  the  true  or  the  pseudo-type.  There  being  room 
for  some  doubt  as  to  how  convergence  of  myopic  eyes  is 
effected,  the  illustration  (Plate  XXXII.)  shows  the  third  con- 
jugate and  the  right  and  left  third  basal  centers,  all  connect- 
ed with  the  interni,  each  doing  a  part  of  the  work.  However 
this  may  be,  the  work  is  abnormal,  and  the  myopic  error 
causing  it  should  be  corrected — not  under-corrected  nor 
over-corrected.  The  myopia  of  orthophoric  eyes,  as  shown 
in  the  distance  test,  should  always  be  fully  corrected.  An- 
other argument  in  favor  of  the  convergence  of  myopic  eyes 
being  effected  by  the  right  and  left  third  basal  centers  is  the 
fact  that,  with  the  correcting  lenses  on,  the  pseudo-exopho- 
ria  disappears.  The  convergence  and  accommodation  of 
corrected  myopic  eyes  are  correctly  represented  in  Plate 
VIII.  If  the  third  conjugate  center  takes  no  part  in  con- 
vergence except  when  the  tenth  center  is  active,  then  Plate 
XXI.  illustrates  the  convergence,  not  only  of  myopic  eyes, 
but  also  of  presbyopic  eyes.  The  author  is  not  quite  sure 
but  that  Plate  XXI.  should  have  been  substituted  for  Plate 
XXXII.  for  illustrating  the  convergence  of  uncorrected 
myopic  orthophoric  eyes. 

Myopia  with  true  Esophoria. — The  brain  center  and  mus- 
cle activity,  for  distant  vision,  in  this  condition,  is  the  same 
as  in  emmetropic-esophoric  eyes,  and  is  illustrated  in  Plate 


138  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 


AMETROPIA  AND   PSEUDO-HETERORHORIA. 


139 


140  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

XVII.  By  reference  to  this  plate,  it  will  be  seen  that  the 
excited  brain  centers  are  the  right  and  left  fourth  basal,  and 
that  the  muscles  are  the  two  externi.  The  accurate  correc- 
tion of  the  myopia  will  not  modify,  in  the  slightest,  the  eso- 
phoria  for  distance.  The  convergence  of  such  eyes  is  more 
easily  effected  than  if  there  had  been  orthophoria  for  dis- 
tance, for  the  reason  that  the  greater  tonicity  of  the  intern i 
would  effect  a  part  of  the  convergence,  leaving  only  a  re- 
mainder to  be  accomplished  by  the  right  and  left  third  basal 
centers.  The  greater  the  esophoria  for  distance,  the  less 
the  demand  that  would  be  made  on  the  right  and  left  third 
basal  centers  in  near  work.  Only  a  partial  correction  of  the 
myopia  should  be  given  for  near  seeing,  when  there  is  eso- 
phoria for  distance,  for  reason  that  the  complete  correction 
of  the  myopia  would  cure  all  the  pseudo-exophoria,  and 
there  would  be  esophoria  in  the  near  as  in  the  far.  The 
convergence  of  uncorrected  myopia  of  esophoric  eyes  is  il- 
lustrated in  Plate  XXI. ;  that  of  partial  correction  is  shown 
in  Plate  VIII.,  and  that  of  a  full  correction  in  Plate  XVIII. 
No  lenses  at  all  for  near  work  would  be  preferable  to  fully 
correcting  lenses,  for  the  reason  that  over-work  of  the  right 
and  left  third  basal  centers  is  better  borne  than  excitation 
of  the  right  and  left  fourth  basal  centers.  The  ideal  lenses 
for  the  near  use  of  myopic-esophoric  ej-es,  are  those  that 
will  give  orthophoria  in  the  near  test.     Such  lenses  allow 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  141 

enough  pseudo-exophoria  to  remain  to  neutralize  the  in- 
trinsic esophoria. 

Myopia  with  true  Exophoria. — The  excited  brain  centers 
and  active  muscles,  when  the  gaze  of  myopic-exophoric  eyes 
is  direct  and  at  infinity,  are  shown  in  Plate  XXI.  This  Plate 
also  shows  that  the  right  and  left  third  basal  centers  are 
excited  and  the  two  interni  are  contracting  to  prevent  di- 
plopia of  emmetropic-exophoric  eyes.  If  it  were  possible 
for  the  third  conjugate  center  to  act  independently  of  the 
tenth  conjugate  center,  which  is  a  matter  for  doubt,  then 
the  exophoria  of  both  emmetropic  and  myopic  eyes,  whose 
gaze  is  direct  and  at  infinity,  might  be  counteracted  by  this 
(the  third)  conjugate  center,  for  the  contraction  of  each 
internus,  under  such  a  condition,  would  be  the  same  as  that 
of  the  other.  This  effort  of  brain  center  and  muscles  would 
be  illustrated  by  Plate  XXXIII.  If  the  teaching  concerning 
the  distant  vision  of  emmetropic-exophoric  eyes,  as  illus- 
trated in  Plate  XXL,  is  true,  then  the  same  teaching  con- 
cerning the  distant  vision  of  myopic-exophoric  eyes  must 
also  be  true.  The  only  alternative  is  the  teaching  of  Plate 
XXXIII.,  and  it  would  be  applicable  alike  to  the  exophoria 
of  both  emmetropic  and  myopic  eyes.  Plate  XXXIII.  is 
introduced  here,  but  is  not  indorsed. 

The  correction  of  myopia  will  sharpen  vision,  but  will  not 
alter  the  muscle  relationship  so  long  as  the  gaze  is  fixed  on 
a  distant  object,  therefore  the  right  and  left  third  basal  cen- 


142  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

ters  and  the  two  interni  must  do  the  same  work  whether 
the  correcting  lenses  are  worn  or  not.  In  the  near  use  of 
uncorrected  myopic  eyes  which  have  true  exophoria,  there 
is  a  greatly  increased  demand  for  activity  on  the  part  of  the 
right  and  left  third  basal  centers,  for  not  only  must  the  true 
exophoria  be  corrected  by  these  centers,  but  also  the  pseudo- 
exophoria.  The  following  case  may  be  supposed,  though 
often  real:  The  myopia  is  3-D  and  the  true  exophoria  is  6°. 
In  distant  vision  the  right  and  left  third  basal  centers  must 
discharge  enough  neuricity  to  the  interni  to  counteract  the 
6°  of  exophoria.  In  near  vision  there  is  still  the  6°  of  true 
exophoria,  and  added  to  this  there  is,  approximately,  6°  of 
pseudo-exophoria,  making  twelve  in  all.  Since  all  of  this 
must  be  counteracted  by  the  right  and  left  third  basal 
centers,  it  must  appear  that  in  near  vision  these  cen- 
ters have  to  do  twice  the  work  demanded  of  them  in 
distant  vision.  Correcting  the  myopia,  and  thereby  cur- 
ing the  pseudo-exophoria,  leaves  only  the  true  exo- 
phoria to  be  counteracted  by  activity  of  the  right  and 
left  third  basal  centers,  when  these  eyes  are  engaged  in 
near  work.  Plate  XXI.  illustrates  the  centers  and  mus- 
cles that  are  active  in  the  near  use  of  these  supposed 
eyes,  the  myopia  being  uncorrected,  it  being  only  necessary 
to  remember  that  the  activity  of  these  centers  in  distant 
vision  is  doubled  in  near  vision.  Plate  XXII.  illustrates  the 
near  use  of  this  same  pair  of  eyes,  the  myopia  having  been 


AMETROPIA  AND   PSEUDO-HETEROPHORIA.  143 

fully  corrected.  The  concave  lenses  have  made  these  eyes 
emmetropic,  but  there  remains  unchanged  the  true  exopho- 
ria.  If  an  over-correction  of  the  myopia  has  been  given,  if 
— 6-D  lenses  have  been  given,  when  the  myopia  is  only  3-D, 
all  the,  pseudo-exophoria  has  been  cured,  and  the  true  exo- 
phoria  has  been  fully  counteracted  by  the  newly  developed 
pseudo-esophoria.  Under  the  influence  of  this  over-cor- 
rection the  interni  act  only  under  the  impulse  sent  them 
from  the  third  conjugate  center,  in  harmony  with  the  ac- 
tivity of  the  tenth  conjugate  center  and  the  ciliary  muscles, 
as  illustrated  in  Plate  VIII.,  but  the  third  and  tenth  con- 
jugate centers  are  doing  twice  the  work  demanded  of  them 
in  the  convergence-accommodation  of  emmetropic  eyes.  An 
over-correction  of  myopia,  when  there  is  exophoria,  is  often 
attended  by  more  comfort  than  a  simple  full  correction. 
There  appears  to  be  no  reason  for  this  other  than  the  fact 
that  the  over-correction  relieves,  in  part  or  in  whole,  the 
right  and  left  third  basal  centers  in  both  distant  and  near 
vision,  while  a  full  correction  leaves  the  work  of  correcting 
all  the  true  exophoria,  in  both  distant  and  near  vision,  to 
these  basal  centers.  This  experience,  which  is  common, 
would  show  that  the  conjugate  centers  have  greater  power 
of  endurance  than  the  basal  centers.  As  to  the  interni,  they 
must  do  the  same  contracting,  whether  stimulated  wholly 
by  either  the  basal  centers  or  the  conjugate  center,  or  in 
part  by  each  of  these  centers.     If  these  muscles  do  their 


144  AMETROPIA   AND   PSEUDO-HETEROPHORIA. 

work  better  and  more  comfortably  under  the  influence  of 
the  third  conjugate  center,  than  under  the  influence  of  the 
right  and  left  third  basal  centers,  then  the  exhaustion  would 
appear  to  come  from  activity  of  the  basal  brain  centers, 
and  not  from  muscle  contraction.  To  relieve  the  right  and 
left  third  basal  centers  in  the  distant  and  near  use  of  myo- 
pic-exophoric  eyes,  it  is  not  best  to  give  an  over-correction 
of  the  myopia,  because  that  involves  the  tenth  and  third 
conjugate  centers  in  an  excessive  amount  of  work,  which 
they  might  bear  well  for  a  time,  but  under  which  they  must 
finally  break  down.  Nor  does  the  over-correction  bring  any 
rest  to  the  interni.  The  rational  treatment  of  such  eyes 
is  to  cure  all  the  pseudo-exophoria  by  fully  correcting  the 
myopia,  demanding  that  the  lenses  shall  be  worn  through- 
out all  working  hours,  and  cure  by  exercise  or  operations 
the  true  exophoria.  This  would  bring  to  such  eyes,  in  dis- 
tant vision,  the  restfulness  of  brain  centers  and  muscles 
shown  in  Plate  VII. ;  and  the  near  vision  (convergence-ac- 
commodation) would  be  attended  by  normal  activity  of  the 
tenth  and  third  conjugate  centers  and  the  ciliary  and  inter- 
nal recti  muscles,  illustrated  in  Plate  VIII. 

If  it  is  possible  for  the  third  conjugate  center  to  help  the 
right  and  left  third  basal  centers,  independent  of  the  tenth 
conjugate  center,  in  converging  myopic-exophoric  eyes,  the 
myopia  being  uncorrected,  then  Plate  XXXII.  would  il- 
lustrate the  activity  of  the  third  conjugate  and  the  right 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  145 

and  left  third  basal  centers,  and  the  interni,  in  their  work  of 
converging  such  eyes.  Even  if  this  illustration  were  cor- 
rect, it  would  not  change  the  correct  method  of  treatment 
of  such  cases,  that  is,  fully  correct  the  myopia  and  thus  cure 
the  pseudo-exophoria,  which  can  exist  only  in  the  near  use 
of  the  eyes;  then  by  exercise  or  operations  cure  the  true 
exophoria  which  exist  in  both  far  and  near  use  of  the  eyes. 
How  to  do  the  one  or  the  other  is  fully  set  forth  in  Ophthal- 
mic Myology,  in  the  chapter  on  exophoria. 

HYPEROPIA. 

Hyperopia  and  Orthophoria. — In  hyperopia  there  is  al- 
ways a  pseudo-esophoria  in  both  distant  and  near  seeing, 
the  quantity  of  this  pseudo  error  being  about  2°  for  each 
1-D  of  the  hyperopia.  All  other  muscle  errors  associated 
with  hyperopia  are  true  or  intrinsic. 

Plate  XXXIV.  represents  hyperopic-orthophoric  eyes  and 
the  conjugate  and  basal  centers  that  are  excited,  and  the 
muscles  that  must  contract,  in  the  interest  of  sharp  seeing 
and  binocular  single  vision.  The  object  of  fixation  is  at 
practical  infinity  and  in  line  of  intersection  of  the  extended 
horizontal  and  median  fixed  planes  of  the  head.  The  tenth 
conjugate  center  is  excited,  in  order  that  the  ciliary  muscles 
may  cause  well  defined  images  to  be  formed  on  the  two 
retinas.  There  being  lateral  orthophoria,  the  visual  axes 
would  be  properly  related  without  any  impulse  being  sent 

10 


146  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

*        S  1         ? 


AMETROPIA  AND   PSEUDO-HETEROPHORIA.  147 

from  either  cortical  or  basal  centers,  but  excitation  of  the 
tenth  conjugate  center  would  have  associated  with  it  excita- 
tion of  the  third  conjugate  center.  This  associated  activity 
of  the  third  conjugate  center  would  make  the  interni  con- 
tract, and  this  would  cause  the  visual  axes  to  cross  between 
the  object  of  fixation  and  the  eyes,  resulting  in  double  vis- 
ion, but  for  the  fact  that  the  fusion  faculty  of  the  mind 
calls  into  simultaneous  action  the  right  and  the  left  fourth 
basal  centers,  in  the  interest  of  binocular  single  vision. 
These  basal  centers  would  send  enough  neuricity  to  their 
respective  externi  to  make  them  contract  sufficiently  to  pre- 
vent the  contracting  interni  from  crossing  the  visual  axes 
too  soon.  Two  conjugate  and  two  basal  centers  must  be  for- 
ever actaive,  and  both  ciliary  muscles  and  the  two  internal 
and  two  external  recti  muscles  must  be  in  a  continuous  state 
of  contraction,  when  hyperopic-orthophoric  eyes  are  look- 
ing straight  ahead  into  infinity.  The  brain  and  muscle 
work  of  such  eyes,  in  distant  vision,  may  be  contrasted  with 
the  restfulness  of  both  brain  and  muscles  when  eyes  are 
emmetropic  and  orthophoric,  by  comparing  Plates  XXXIV. 
and  VII. 

That  the  esophoria  shown  in  Plate  XXXIV.  is  pseudo,  and 
not  true,  is  made  evident  by  the  fact  that  a  correction  of 
the  hyperopia  will  cause  the  esophoria  to  disappear.  It 
is  probable  that  hyperopia  causes  symptoms,  not  so  much 
because  of  excitation  of  the  tenth  and  third  conjugate  cen- 


148  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

ters,  but  because  of  the  work  that  the  right  and  the  left 
fourth  basal  centers  must  do  to  prevent  diplopia.  Proof  of 
this  statement  will  appear  in  the  study  of  hyperopic-exo- 
phoric  eyes. 

A  full  correction  of  the  hyperopia  shown  in  Plate 
XXXIV.  relieves  the  tenth  conjugate  center  of  any  necessity 
for  action.  This  allows  the  third  conjugate  center  to  cease 
discharging  neuricity  to  the  interni,  hence  there  can  be  no 
longer  any  need  for  activity  of  the  right  and  left  fourth 
basal  centers.  Simple  convex  lenses  would  bring  to  hyper- 
opic-orthophoric  eyes,  in  distant  vision,  the  restfulness  of 
brain  centers  and  muscles  of  emmetropic-orthophoric  eyes 
shown  in  Plate  VII.  Nothing  more  could  be  desired ;  noth- 
ing less  should  be  done. 

Plate  XXXIV.  not  only  shows  what  brain  centers  and 
muscles  must  be  active  in  the  distant  vision  of  hyperopic- 
orthophoric  eyes,  but  it  also  shows  that  the  same  centers 
and  muscles  must  be  active  in  near  vision.  Any  work  on 
the  part  of  these  centers,  in  distant  seeing,  is  over-work,  or 
strain,  hence  the  near  use  of  such  eyes  must  also  be  attend- 
ed by  over-work,  or  strain.  The  convex  lenses  for  the  cor- 
rection of  the  hyperopia  makes  near  work  easy,  in  that 
the  right  and  left  fourth  basal  centers  will  be  entirely  re- 
lieved and  the  tenth  and  third  conjugate  centers  will  have 
to  do  only  normal  work.     So  far  as  near  work  is  concerned, 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  149 

the  correction  of  the  hyperopia  converts  Plate  XXXIV. 
into  Plate  VIII. 

It  will  be  observed  that  the  same  basal  and  conjugate 
centers  are  active  in  the  distant  and  near  vision  of  hyper- 
opic-orthophoric  eyes  as  are  active  in  the  near  use  of  em- 
metropic,-esophoric  eyes,  for  Plate  XXXIV.  is  the  same  as 
Plate  XVIII.  The  difference  in  the  character  of  the  work 
done  cannot  be  shown  in  a  plate.  In  each  plate  the  work 
done  by  the  two  fourth  basal  centers  and  the  two  externi 
is  abnormal  work,  or  strain;  in  plate  XVIII.,  the  work  of 
the  tenth  and  third  conjugate  centers  and  the  ciliary  mus- 
cles and  the  interni  is  normal  work,  but  in  Plate  XXXIV. 
the  work  of  these  conjugate  centers  is  abnormal,  and  there- 
fore is  strain. 

So  long  as  there  is  any  power  to  accommodate,  no  cor- 
rection of  hyperopia  should  be  attempted  without  the  aid 
of  a  cycloplegic. 

Hyperopia  and  True  Esophoria. — Plate  XXXIV.,  used 
for  illustrating  hyperopic-orthophoric  eyes,  in  both  distant 
and  near  seeing,  must  also  be  used  for  showing  the  brain 
centers  that  are  active  and  the  muscles  which  are  made  to 
contract,  in  both  the  far  and  near  seeing  of  hyperopic- 
esophoric  eyes.  The  hyperopia  being  the  same  in  the  two 
cases,  the  tenth  and  third  conjugate  centers  do  no  more  in 
the  one  case  than  in  the  other,  but  in  the  hyperopic-eso- 
phoric  case  the  right  and  left  fourth  basal   centers  are 


150  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

doubly  taxed — that  is,  they  must  send  neuricity  to  the  ex- 
terni  to  counteract  the  pseudo-esophoria  caused  by  the  hy- 
peropia, and  they  must  also  supply  these  muscles  with  the 
force  necessary  for  counteracting  the  intrinsic  esophoria. 
This  excessive  draft  on  the  right  and  left  fourth  basal  cen- 
ters must  be  kept  up  in  near  vision  as  well  as  in  far,  there- 
fore there  is  no  rest  during  all  the  waking  hours.  If  there 
is  true  esophoria  4°,  and  pseudo-esophoria  4°,  the  total  to 
be  counteracted  by  the  basal  centers  is  8°.  The  correc- 
tion of  the  hyperopia,  by  proper  lenses,  cures  the  4°  of 
pseudo-esophoria,  but  still  leaves  the  burden  of  counter- 
acting the  4°  of  true  esophoria  on  the  right  and  left  fourth 
basal  centers.  This  correction  of  the  hyperopia  converts 
Plate  XXXIV.  into  XVIII. ,  so  far  as  distant  vision  is  con- 
cerned, in  which  the  only  active  centers  are  the  right  and 
left  fourth  basal.  Even  with  the  hyperopia  corrected,  the 
near  use  of  these  eyes  would  still  be  illustrated  by  Plate 
XXXIV.,  although  now  these  basal  centers  must  counteract 
only  the  true  esophoria. 

That  it  is  the  activity  of  the  right  and  left  fourth  basal 
centers,  and  the  consequent  contraction  of  the  externi,  that 
produces  the  various  symptoms  of  which  such  patients  com- 
plain, and  not  the  associated  activity  of  the  tenth  and  third 
conjugate  centers,  and  the  consequent  contraction  of  the 
ciliary  muscles  and  the  internal  recti,  seems  clear,  in  the 
light  of  the  fact  hat  the  same  hyperopia  associated  with 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  151 

4°  of  true  exophoria,  rarely  causes  any  trouble  at  all.  This 
latter  condition  furnishes  only  enough  pseudo-esophoria  to 
neutralize  the  true  exophoria,  hence  no  basal  center  is 
active,  as  shown  in  Plate  XXXV.  The  result  of  treatment 
also  points  to  the  fact  that  the  basal  centers  are  the  source 
of  symptoms.  A  correction  of  the  hyperopia  associated  with 
true  esophoria  brings  great  relief,  although  there  is  still  left 
some  work  for  the  right  and  lefth  fourth  basal  centers  to 
do,  in  both  far  and  near  seeing.  Correction  of  the  hy- 
peropia associated  with  exophoria,  at  once  calls  into  action 
the  right  and  left  third  basal  centers,  in  both  distant  and 
near  seeing,  to  counteract  the  true  exophoria,  and  discom- 
fort, before  unknown,  arises.  In  each  of  these  cases  the 
tenth  and  third  conjugate  centers  have  been  relieved  alike 
of  the  necessity  for  abnormal  work,  but  in  the  former  case 
half  the  burden  has  been  removed  from  the  right  and  left 
fourth  basal  centers,  while  in  the  latter  a  new  demand  on 
the  right  and  left  third  basal  centers  has  been  created. 

That  hyperopia  is  one  of  the  causes  of  esotropia  is 
proved  by  the  well  known  fact  that  a  full  correction  of  this 
focal  error,  soon  after  squint  has  manifested  itself,  will 
allow  the  eyes  to  swing  straight  again.  That  many  cases 
of  esotropia  have  ben  caused  by  hyperopia  alone  may  be 
doubted,  though  a  high  degree  of  this  focal  error  might  do 
so.  If  the  lateral  muscles,  in  a  given  case,  are  well  bal- 
anced, each  fourth  basal  center  should  be  able  to  produce 


152  AMETROPIA   AND   PSEUDO-HETEROPHORIA. 

8°  of  abduction.  Every  dioptre  of  hyperopia  causes  near- 
ly 2°  (1.8°)  of  pseudo-esophoria,  hence  4  D.  of  hyperopia 
would  cause  8°  (7.2°)  of  pseudo-esophoria,  which  should 
be  counteracted  by  normal  externi,  in  the  interest  of  binoc- 
ular single  vision.  A  much  higher  degree  of  hyperopia 
alone  could  cause  an  esotropia,  for  the  resultant  pseudo- 
esophoria  would  be  greater  than  the  fourth  basal  centers 
and  their  externi  can  counteract.  Usually  the  fundamental 
cause  of  esotropia  is  true  esophoria;  but  it  would  take  8° 
or  more  of  this  error,  unaided,  to  cause  internal  squint.  In 
the  greater  number  of  cases  true  esophoria  and  pseudo- 
esophoria  constitute  the  twin  causes  of  esotropia.  Either 
one  of  these  errors  alone  might  be  counteracted  by  the 
action  of  the  right  and  left  fourth  basal  centers  on  their 
respective  externi.  The  task  of  counteraction,  except  in 
rare  cases,  is  always  undertaken  by  the  fusion  faculty  of 
the  mind,  and  often  the  work  is  maintained  throughout 
life;  but  not  infrequently  the  fourth  basal  centers  become 
exhausted ;  and,  refusing  to  respond  longer,  the  interni  are 
allowed  to  cross  the  visual  axes.  After  an  interval  of  rest 
these  centers  sometimes  reassert  themselves,  and,  for  a 
short  period,  straighten  the  eyes  again,  to  once  more  fail 
after  another  period  of  exhaustive  work.  Finally  the 
squint  becomes  fixed,  and  thereafter  the  fourth  basal  cen- 
ters remain  as  inactive  as  in  orthophoria.  Usually  this 
occurs  so  early  in  life  (between  the  ages  of  one  and  three 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  153 

years)  that  the  power  of  mental  suppression  may  be  ac- 
quired. Thus  the  patient  loses  the  power  of  binocular  vi- 
sion, but  he  gains  in  comfort — not  that  the  conjugate  cen- 
ters have  less  to  do,  but  because  the  basal  centers  have 
lapsed  into  rest.  So  long  as  esotropia  is  comitant  there  is 
comparative  comfort ;  but  there  is  also  disfigurement. 

The  treatment  of  hyperopic-esophoric  eyes  should  be  so 
directed  as  to  bring  complete  rest  to  the  right  and  left  fourth 
basal  centers,  regardless  of  the  point  of  view;  it  should  also 
give  rest  to  the  tenth  and  third  conjugate  centers,  and  their 
respective  muscles,  in  distant  vision,  so  that  near  work 
may  be  accomplished  by  only  a  normal  expenditure  of  nerve 
force  and  muscle  energy.  First  of  all,  the  hyperopia  should 
be  corrected,  while  the  eyes  are  under  the  influence  of  a 
cycloplegic,  for  in  no  other  way  can  it  be  accurately  done. 
The  convex  lenses  at  once  accomplish  the  work  of  complete- 
ly relieving  the  tenth  and  third  conjugate  centers,  and  the 
ciliary  muscles  and  the  internal  recti,  from  the  necessity 
of  doing  any  abnormal  work.  So  far  as  these  centers  and 
muscles  are  concerned,  the  lenses  will  give  the  same  rest 
in  distant  vision,  illustrated  in  Plate  VII.  Only  the  pseudo- 
esophoria,  in  both  far  and  near  vision,  can  be  cured  by  the 
convex  lenses ;  hence  these  lenses  can  relieve,  only  partially, 
the  right  and  left  fourth  basal  centers,  and  their  respective 
external  recti.  The  correcting  lenses  would  leave  such  eyes, 
so  far  as  distant  vision  is  concerned,  in  the  condition  illus- 


154  AMETROPIA   AND   PSEUDO-HETEROPHORIA. 

trated  in  Plate  XVII. ,  in  which  the  right  and  left  fourth 
basal  centers  must  force  the  weak  externi  to  counteract  the 
excesive  tonicity  of  the  interni.  That  the  cure  may  be  com- 
plete, the  weak  externi  must  be  developed  by  rhythmic  ex- 
ercise, or  they  must  be  strengthened  by  the  shortening 
operation;  or  the  tonicity  of  the  interni  must  be  reduced 
by  partial  tenotomy.  The  aim  of  either  means  is  to  make 
the  tonicity  of  the  externi  equal  the  tonicity  of  the  interni. 
No  part  of  the  pseudo-esophoria  can  be  corrected  by  any 
kind  of  exercise,  and  certainly  no  part  of  it  should  ever  be 
corrected  by  any  kind  of  operation.  Lenses  for  the  hyper- 
opia and  pseudo-esophoria,  and  exercise  or  operations  for 
the  true  esophoria,  will  convert  hyperopic-esophoric  eyes 
into  emmetropic-orthophoric  eyes.  The  restfulness  of 
brain  centers  and  muscles,  in  distant  vision,  resulting  from 
the  treatment  outlined  above,  of  hyperopic-esophoric  eyes, 
is  correctly  shown  in  Plate  VII.  The  change  wrought  can 
be  easily  understood  by  comparing  Plates  XXXIV.  and  VII. 
The  near  use  of  eyes  thus  fully  corrected  is  illustrated  in 
Plate  VIII.  If  only  the  hyperopia  and  the  pseudo-esopho- 
ria have  been  corrected  by  the  lenses,  the  true  esophoria 
remaining,  the  near  use  of  these  eyes  would  be  shown  in 
Plate  XVIII.  In  Plates  VIII.  and  XVIIL,  the  tenth  and 
third  conjugate  centers  are  doing  precisely  the  same  work, 
but  in  the  former  plate  the  right  and  left  fourth  basal  cen- 


AMETROPIA  AND   PSEUDO-HETEROPHORIA.  155 

ters  are  at  rest,  while  in  the  latter  plate  these  two  centers 
are  excited  that  the  true  esophoria  may  be  counteracted. 

While  true  esophoria  cannot  be  lessened  by  any  lens,  so 
far  as  distant  vision  is  concerned,  a  pseudo-exophoria  in 
the  near  may  be  created  by  the  wearing  of  presbyopic 
lenses,  or  lenses  that  over-correct  the  hyperopia.  The 
presbyopic  lenses  lessen  the  demand  on  the  tenth  conjugate 
center,  and  an  associated  smaller  demand  is  made  on  the 
third  conjugate  center.  This  allows  the  convergence  to  be 
effected  largely  by  tonicity,  and  the  right  and  left  fourth 
basal  centers  are  relieved  correspondingly.  But  to  give 
presbyopic  lenses  while  one  is  yet  young  is  not  the  best 
thing  to  do.  It  would  be  justified  only  by  the  refusal  of 
the  patient  to  submit  to  the  exercise  or  operative  treatment 
of  the  true  esophoria. 

Whenever  the  esophoria  of  hyperopic  eyes  has  been 
converted  into  an  esotropia,  the  correction  of  the  hyperopia 
should  not  be  delayed  even  though  the  patient  might  be  only 
two  years  old.  The  eyes  have  crossed  because  the  right 
and  left  fourth  basal  centers,  exhausted  by  overwork,  have 
given  up  the  task  of  supplying  the  external  recti  with  the 
neuricity  necessary  for  counteracting  the  pseudo-  and  in- 
trinsic esophoria.  Either  one  of  these  errors  existing  alone 
might  have  been  counteracted  by  the  fourth  basal  centers 
acting  on  the  externi,  but  the  sum  of  the  two  errors  caused 
so  great  demands  on  these  centers  and  their  muscles,  in  the 


156  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

interest  of  binocular  single  vision,  that  it  was  only  a  ques- 
tion of  a  short  time  until  they  would  fail  to  respond. 
Doubtless  the  power  of  mental  suppression  of  the  image  in 
the  crossed  eye  had  been  acquired  previously;  for  the  mind 
has  two  methods  of  preventing  diplopia :  one,  the  fusion  of 
images  by  the  exercise  of  the  fusion  faculty  on  basal  cen- 
ters, when  there  is  abnormal  adjustment;  the  other,  mental 
suppresion  of  one  image  when  the  two  cannot  be  fused. 

The  power  to  suppress  entirely  and  continuously  the 
macular  image  in  one  eye  can  be  acquired  only  in  early 
years,  and  then  only  because  the  two  maculas  must  lose 
their  proper  relationship.  The  development  of  the  mental 
suppression  makes  it  easy  for  the  fusion  faculty  to  lose  its 
control  over  all  basal  centers.  This  control  being  lost,  all 
the  basal  centers  lapse  into  a  state  of  restfulness  as  com- 
plete as  if  the  two  eyes  were  orthophoric  and  emmetropic. 
Each  cortical,  or  conjugate,  center  continues  to  discharge 
neuricity  to  its  two  muscles,  just  as  it  did  before  the  eyes 
crossed,  and  just  as  it  does  when  there  is  orthophoria, 
hence  the  two  eyes,  although  crossed,  move  comitantly. 

Every  attempt  to  re-establish  binocular  single  vision, 
without  bringing  discomfort  to  the  patient,  should  aim  at 
a  cure  of  both  the  pseudo-esophoria  and  the  true  esophoria. 
The  amblyoscope,  used  early  and  persistently,  a  fight 
against  mental  suppression,  only  helps  the  fusion  faculty  to 
maintain  its  mastery  over  the  right  and  left  fourth  basal 


AMETROPIA   AND   PSEUDO-HETEROPHOIUA.  157 

centers;  but  this  would  be  like  forcing,  with  a  whip,  the 
weaker  horse  of  a  pair  to  draw  its  part  of  a  heavy  load. 
Fusion  is  always  effective  when  the  maculas  are  properly- 
related,  whether  by  muscle  tonicity  or  muscle  contractility. 
To  regulate  the  tonicity  of  muscles  is  the  way  to  get  easy 
fusion  of  images.  The  pseudo-esophoria  corrected  by  con- 
vex lenses,  and  the  true  esophoria  cured  by  operations,  gives 
the  best  chance  for  easy  fusion,  and  the  only  chance  for 
comfortable  binocular  single  vision.  The  amblyoscope,  as 
used  by  Worth  and  others  who  follow  him,  is  but  a  means 
of  awakening  the  mind  to  the  fact  that  it  has  two  eyes 
which  it  may  use.  The  time  to  use  this  agent  is  after  the 
hyperopia  has  been  corrected,  when  the  fourth  basal  cen- 
ters may  be  made  to  take  up  the  work  of  counteracting  only 
the  true  esophoria,  the  pseudo-esophoria  having  already 
been  cured.  After  a  partial  recovery  from  the  mental 
blindness,  the  esophoria  should  be  corrected  so  that,  ever 
after,  binocular  single  vision  may  be  maintained  without 
activity  of  basal  centers,  and  without  abnormal  action  of 
ocular  muscles.  For  a  fuller  study  of  esotropia  the  reader 
is  again  referred  to  Ophthalmic  Myology. 

Hyperopia  and  Exophoria. — Hyperopia  often  exists  in 
cases  in  which  the  externi  are  intrinsically  stronger  than 
the  interni,  but,  notwithstanding,  this  hyperopia  is  the 
cause  of  pseudo-esophoria.  Plate  XXXV.  represents  such 
a  pair  of  eyes  engaged  in  either  far  or  near  seeing,  the 


158  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

J? 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  159 

point  of  fixation  being  on  the  line  of  intersection  of  the 
extended  median  and  horizontal  planes  of  the  head.  Per- 
fect images  of  an  object,  either  in  the  distance  or  near  by, 
can  be  formed  on  the  retinas  only  as  a  result  of  excitation 
of  the  tenth  conjugate  center.  There  must  be  associated 
activity  of  the  third  conjugate  center  and  consequent  con- 
traction of  the  interni.  This  activity  of  the  interni,  ex- 
cited by  the  third  conjugate  center,  counteracts,  in  part  or 
wholly,  the  true  exophoria,  thus  relieving  the  right  and  left 
third  basal  centers  of  the  necessity  of  counteracting  this 
error.  If,  in  a  given  case,  there  is  exophoria  4°,  and  hy- 
peropia 2  D,  the  pseudo-esophoria  will  be  4°,  the  latter 
counteracting  the  former.  The  association  of  hyperopia 
with  exophroia  is  a  fairly  comfortable  condition,  as  com- 
pared with  the  association  of  emmetropia  with  exophoria ; 
and  this  is  explainable  only  on  the  ground  that,  in  the  for- 
mer, only  conjugate  centers  are  active,  while  in  the  latter 
basal  centers  must  do  the  counteracting  of  the  exophoria. 
A  correction  of  the  hyperopia  of  eyes  truly  exophoric  con- 
verts Plate  XXXV.  into  Plates  XXI.  and  XXII.,  in  each  of 
which  the  right  and  left  third  basal  centers  are  represented 
as  actively  counteracting  true  exophoria.  Plate  XXI.  rep- 
resents the  eyes  as  looking  into  practical  infinity,  the  only 
active  brain  centers  being  the  right  and  left  third  basal, 
and  the  only  contracting  muscles,  the  two  interni.  Plate 
XXII.  represents  the  eyes  engaged  in  near  work,  the  tenth 


163  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

and  third  conjugate  centers  doing  normal  work,  while  the 
right  and  left  third  basal  centers  are  combatting  the  exo- 
phoria. 

The  treatment  of  hyperopic-exophoric  eyes  should  be  di- 
rected, first,  towards  the  correction  of  the  exophoria,  and 
should  be  either  operative,  or  by  exercise  of  the  interni.  If 
the  muscles  have  been  subjected  to  operations — partial 
tenotomies  of  the  externi  of  shortenings  of  the  interni — 
then  a  full  correction  of  the  hyperopia  should  be  given,  thus 
converting  the  condition  shown  in  Plate  XXXV.  into  the 
condition  shown  in  Plate  VII.  If  the  treatment  of  the 
exophoria  is  by  exrcise,  as  the  interni  gain  in  tone,  a  part 
of  the  hyperopia  should  be  corrected;  and  from  time  to 
time,  as  the  work  of  developing  the  interni  goes  on,  still 
stronger  lenses  should  be  given,  finally  attaining  the  point 
of  full  correction  only  when  there  is  no  longer  any  exo- 
phoria. To  correct  the  hyperopia  and  ignore  the  exophoria 
will  bring  discomfort  to  the  patient  whenever  the  correct- 
ing lenses  are  worn. 

Every  error  of  refraction  should  be  carefully  and  accu- 
rately studied  while  the  eyes  are  under  the  influence  of  a 
mydriatic,  or,  more  correctly  speaking,  a  cycloplegic,  unless 
advancing  years  have  already  robbed  the  ciliary  muscles 
of  their  power.  Before  the  cycloplegic  is  used  the  tonicity 
tests  of  all  the  extrinsic  ocular  muscles  should  be  made  and 
recorded;  but  only  the  lateral  recti  would  respond  differ- 


AMETROPIA   AND   PSEUDO-HETEROPHORIA.  161 

ently  after  the  eyes  have  gone  under  the  influence  of  the 
drug.  No  tonicity  test  of  the  lateral  recti  can  be  relied 
upon  if  made  while  the  eyes  are  under  the  influence  of  a 
cycloplegic.  If,  in  the  tonicity  test  of  the  lateral  muscles, 
there  is  esophoria  of  4°,  it  cannot  be  known  whether  it  is 
pseudo-  or  true  until  the  refraction  has  been  studied.  If 
the  eyes  prove  to  be  emmetropic,  then  the  whole  of  the  error 
is  intrinsic,  and  the  same  is  true  if  there  is  myopia  of  any 
quantity ;  but,  if  the  eyes  are  hyperopic,  the  esophoria  shown 
is  the  sum  of  the  pseudo-  and  intrinsic  errors,  if  not  en- 
tirely pseudo.  If  the  hyperopia  is  2  D,  the  4°  of  esophoria 
is,  practically,  all  pseudo-esophoria.  Every  pair  of  convex 
spherical  lenses  given  either  cures  a  pseudo-esophoria,  in 
both  the  far  and  near,  or  causes  a  pseudo-exophoria  in  the 
near ;  every  pair  of  concave  lenses  given  either  cures  an  ex- 
isting pseudo-exophoria  in  the  near  or  causes  a  pseudo- 
esophoria  in  both  far  and  near.  Hyperopia  should  be  fully 
corrected  for  both  distant  and  near  seeing  only  when  the 
lateral  muscles  are  well  balanced  or  when  there  is  intrinsic 
esophoria;  an  over-correction  of  hyperopia,  in  the  near, 
should  never  be  made  unless  there  is  intrinsic  esophoria. 
When  there  is  true  exophoria,  hyperopia  should  not  be  cor- 
rected, or,  at  most,  only  a  partial  correction  should  be 
given. 

Regardless  of  the  state  of  the  lateral  muscles,  myopia 
should  be  fully  corrected  for  distant  seeing;  and  a  full  cor- 


162  AMETROPIA  AND   PSEUDO-HETEROPHORIA. 

rection  should  be  worn  in  near  work,  also,  when  there  is 
perfect  balance  of  the  lateral  recti  muscles,  or  when  there 
is  true  exophoria.  No  correction,  or,  at  most,  only  a  par- 
tial correction,  should  be  worn  in  near  work,  when  there  is 
true  esophoria.  In  true  exophoria  an  over-correction  of 
myopia  often  gives  comfort  to  the  wearer,  for  all  distances. 
To  prescribe  spherical  lenses  without  a  knowledge  of  the 
condition  of  the  lateral  recti  muscles  should  be  condemned. 


CHAPTER   IV. 


COMPENSATING  HETEROTROPIA. 


Compensating  heterotropia  is  an  actual  turning  or  tor- 
sioning  of  one  or  both  eyes,  in  order  that  there  may  be 
binocular  single  vision.  Whatever  may  be  the  form  of  this 
error,  the  muscle  that  does  the  turning  or  torting  is  made 
to  do  so  by  the  action  of  the  fusion  faculty  of  the  mind 
on  the  basal  center  with  which  it  is  connected.  The  work 
done  by  both  basal  center  and  muscle  to  effect  this  turn- 
ing is  the  same  that  is  done  in  heterophoria  to  prevent  a 
turning;  and,  in  each  condition,  the  aim  is  to  prevent 
diplopia.  Compensating  heterotropia  may  be  excited  by 
either  natural  or  artificial  conditions;  but,  whether  natural 
or  artificial,  the  condition  is  such  as  would  produce  diplopia, 
if  not  corrected. 

Natural   Causes. 

Anisometropia. — Unequal  hyperopia  or  myopia  of  the  two 
eyes,  or  hyperopia  of  one  eye  and  myopia  of  the  other, 
must  cause  compensating  heterotropia,  whenever  the  eyes 
are  rotated  from  the  primary,  to  any  secondary,  position. 

(163) 


164 


COMPENSATING   HETEROTROPIA. 


The  eye  that  has  the  greatest  refractive  power,  when  look- 
ing at  a  rectangle,  will  have  the  larger  image  on  its  retina. 
This  is  shown  in  Figure  6,  in  which  the  rectangle  abed 
is  seen  by  the  eye  with  less  refractive  power,  while  the  eye 
of   greater   refraction   sees   the   same   rectangular   figure 


Fig.  6. 


larger,  as  shown  by  rectangle  a"  b"  c"  d".  If  the  head 
is  in  the  primary  position,  and  the  center,  e,  of  the 
rectangle  is  the  point  of  fixation,  there  is  no  need  for  com- 
pensating contraction  of  any  one  muscle  of  an  orthophoric 
set.     If  the  eyes  are  to  be  verted,  so  as  to  fix  any  point 


COMPENSATING    HETEROTROPIA.  165 

on  the  periphery  of  the  rectangle,  the  visual  axis  of  the 
eye,  with  the  smaller  image,  could  not  reach  this  point  in 
harmony  with  its  fellow  eye,  under  the  influence  of  the  voli- 
tional center,  or  centers,  excited ;  for  the  arc  of  rotation  of 
this  eye  is  smaller  than  the  arc  that  must  be  described  by 
the  visual  axis  of  the  eye  with  the  greater  refraction.  To 
move  in  harmony,  the  latter  eye  must  rotate  faster  than  the 
former,  and  this  can  be  done  only  by  means  of  activity 
of  the  proper  basal  center.  This  can  be  better  understood 
by  again  glancing  at  Figure  6.  If  the  second  point  of  view 
is  the  upper  right  hand  corner  of  the  rectangle,  one  visual 
axis  must  move  from  e  to  d,  and  the  other  must  move  from 
e  to  d".  The  eye  (right)  that  has  the  less  refraction  will 
be  rotated,  so  that  the  image  d  may  fall  on  its  macula. 
This  is  accomplished  by  volition  acting  on  the  first,  fourth 
and  eighth  conjugate  centers,  causing  them  to  discharge 
neuricity  to  the  superior  and  external  recti  and  the  superior 
oblique.  The  same  centers,  at  the  same  moment,  will  dis- 
charge an  equal  quantity  of  neuricity  to  the  superior  and 
internal  recti  and  inferior  oblique  of  the  left  eye — the  one 
with  greater  refraction.  Thus  stimulated,  the  visual  axis 
would  move  with  the  same  speed  and  to  the  same  extent  as 
the  axis  of  the  other  eye.  When  the  image  of  the  corner  of 
the  rectangle  falls  on  the  macula  of  the  right  eye,  the  image 
in  the  left  eye  has  not  yet  reached  its  macula,  hence  there 
would  be  diplopia.     To  prevent  the  diplopia  supplemental 


166  COMPENSATING   HETEROTROPIA. 

neuricity  is  sent  by  the  left  first,  third  and  seventh  basal 
centers,  to  the  superior  and  internal  recti,  and  inferior 
oblique,  respectively,  so  that  the  left  visual  axis  may  reach 
d"  at  the  same  moment  that  the  right  visual  axis  reaches  d. 
The  three  volitional  centers  act  from  the  beginning  to  the 
end  of  the  oblique  right  version,  and  the  same  is  true  of  the 
three  left  basal  centers.  In  such  a  case  the  basal  centers 
get  no  rest  except  when  the  eyes  are  in  their  primary  po- 
sitions. 

In  direct  right  and  left  version  of  eyes  of  unequal  refrac- 
tion, only  one  basal  center  would  be  excited  at  a  time;  in 
superversion,  two  basal  centers  would  be  excited,  and  the 
same  would  be  true  of  subversion. 

In  anisometropia  the  basal  centers  should  be  relieved  of 
the  work  required  of  them.  This  can  be  done  by  the  full 
correction  of  the  error  found  in  each  eye.  For  all  practical 
purposes  the  lenses  would  make  the  two  images  equal  in 
size,  therefore  there  would  be  no  further  need  for  activity 
of  any  basal  center,  or  abnormal  contraction  of  any  ocular 
muscle. 

In  eyes  of  unequal  refraction,  the  ciliary  muscle,  which 
has  to  do  the  most  work,  must  receive  supplemental  neu- 
ricity from  its  tenth  basal  center.  Full  correction  of  the 
error  in  each  eye  would  relieve  this  basal  center  also. 

"It   is   more   necessary   to   correct   unequal    refraction, 


COMPENSATING    HETEROTROPIA.  167 

though  the  errors  be  not  great,  than  it  is  to  correct  greater 
errors  that  are  equal  in  the  two  eyes." 

Displaced  Anterior  Pole. — If,  in  one  or  both  eyes,  the 
corneal  center  and  the  anterior  pole  do  not  coincide,  there 
must  be  compensating  heterotopia.  (Displacement  of  the 
macula  and  displacement  of  the  anterior  pole  are  one  and  the 
same  thing.)  If  the  anterior  pole  is  central  in  one  cornea 
and  is  displaced  nasal-ward  in  the  other,  there  must 
be  a  compensating  exotropia;  if  it  is  displaced  temple- 
ward,  there  must  be  a  compensating  esotropia;  if  dis- 
placed upward,  there  must  be  a  compensating  catatropia; 
and  if  displaced  downward,  there  must  be  a  compensating 
hypertropia.  When  the  anterior  pole  is  displaced  nasal- 
ward,  which  can  be  shown  by  the  reflected  image  of  the 
white-bordered  disc  of  the  opthalmometer,  if  the  tonicity 
test  does  not  show  esophoria,  it  is  because  there  is  an  excess 
of  tonicity  of  the  externus.  In  such  a  case  there  is  a 
tonicity  exotropia,  making  unnecessary  a  compensating  con- 
tractile exotropia. 

If  one  eye  is  placed  lower  in  its  orbit  than  its  fellow 
eye,  there  must  be  a  compensating  hypertropia.  The  same 
is  true  when  the  head  is  inclined  to  one  side. 

The  vertical  and  lateral  heterotropias  caused  by  the  dis- 
placed anterior  poles  are  best  treated  by  prisms  in  positions 
of  rest;  that  is,  if  the  anterior  pole  is  nasal-ward,  the 
base  of  the  prism  should  be  out;  if  temple- ward,  the  base 


168  COMPENSATING   HETEROTROPIA. 

should  be  in;  if  up,  the  base  should  be  down;  and  if 
down,  the  base  should  be  up.  It  must  be  remembered  that 
the  guide,  as  to  the  use  of  the  prism  in  these  cases,  is  the 
tonicity  test  of  the  muscles ;  for  an  eye  whose  anterior  pole 
is  nasal-ward,  may  have  an  externus  with  enough  excess 
of  tone  to  properly  relate  the  eyes  without  demand  on  the 
fourth  basal  center.  Indeed,  the  externi  may  be  so  much 
stronger  than  the  interni  as  to  make  such  eyes  exophoric, 
and  in  such  a  case  the  third,  and  not  the  fourth,  basal 
center  must  be  active.  The  heterophorias  of  eyes  with 
decentered  corneas  must  be  treated  as  if  no  decentration 
existed. 

Eyes  whose  anterior  poles  are  several  degrees  nasal-ward 
from  the  corneal  center,  have  the  appearance  of  slight 
external  squint,  and  vice  versa. 

The  compensating  hypertropia  caused  by  one  orbit  being 
lower  than  its  fellow,  should  be  treated  with  a  prism,  base 
up,  provided  the  tonicity  test  shows  cataphoria.  The  lower 
eye  could  have  a  superior  rectus  possessed  of  so  much  tonic- 
ity that  the  test  would  show  hyperphoria. 

The  object  to  be  accomplished  by  a  prism  in  any  form  of 
compensating  heterotopia,  is  to  quiet  a  basal  center  and  re- 
lieve the  orthophoric  eye  from  the  necessity  of  turning; 
the  object  of  the  prism  in  heterophoria  is  to  quiet  a  basal 
center  and  to  allow  the  heterophoric  eye  to  turn  into  the 
position  of  tonicity  of  its  muscles.     In  both  classes  of  cases 


COMPENSATING    HETEROTROPIA.  169 

basal  centers  are  placed  at  rest  by  the  prisms,  and  binocular 
single  vision  is  maintained. 

In  compensating  vertical  heterotropia  a  prism  may  be 
placed  base  up  before  the  lower  eye  or  base  down  before  the 
higher  eye,  or  the  two  may  be  given ;  but  in  vertical  hetero- 
phoria  it  is  always  better  to  use  only  the  prism  base  down 
before  the  hyperphoric  eye,  to  make  it  easier  for  the  su- 
perior oblique  muscle  to  keep  the  vertical  axis  parallel  with 
the  median  plane  of  the  head. 

Compensating  Cyclotropia. — It  is  now  universally  agreed 
that,  in  astigmatism,  every  line  not  in  the  plane  of  the  me- 
ridian of  either  greatest  or  least  curvature,  has  its  image 
displaced  towards  the  meridian  of  greatest  curvature. 
This  displacement  of  the  image  of  a  line  makes  it  impos- 
sible for  the  line  and  the  image  to  lie  in  the  same  plane. 

In  hyperopic  astigmatism,  images  formed  between  the 
two  principal  meridians,  are  always  displaced  towards  the 
meridian  of  greatest  curvature.  This  displacement  of  the 
image  of  a  line  makes  it  impossible  for  the  line  and  the 
image  to  lie  in  the  same  plane.  In  non-astigmatic  eyes  the 
line  and  its  image  are  always  in  the  same  plane;  and  the 
same  is  true  of  the  line  that  lies  in  the  plane  of  either  of 
the  two  principal  meridians  of  an  astigmatic  eye,  but  of  no 
other  line. 

In  hyperopic  astigmatism,  images  formed  between  the 
two  principal  meridians  are  always  displaced  towards  the 


170  COMPENSATING    HETEROTROPIA. 

best  meridian;  in  myopic  astigmatism,  towards  the  worst 
meridian;  and  in  mixed  astigmatism,  towards  the  myopic 
meridian.  In  symmetric  astigmatism — that  is,  when  the 
planes  of  the  meridians  of  greatest  curvature  are  parallel, 
or,  if  horizontal,  they  both  lie  in  the  same  plane,  the  two 
immages  of  a  single  object  will  always  fall  on  corresponding 
retinal  parts,  whether  displaced  or  not,  hence  can  be  fused, 
while  both  vertical  axes  are  still  parallel  with  the  median 
plane  of  the  head. 

Parallel  and  equal  astigmatism  of  orthophoric  eyes  makes 
no  demand  for  compensating  contraction  of  any  ocular  mus- 
cle, for,  without  this,  all  images  are  perfectly  fused.  The 
heterophorias  bear  the  same  relationship  to  hyperopic  astig- 
matic eyes  that  they  do  to  hyperopic  eyes;  and  they  have 
the  same  relationship  with  myopic  astigmatic  eyes  that  they 
have  with  myopic  eyes. 

In  non-symmetric  oblique  astigmatism,  unless  the  best 
meridian  of  one  eye  and  the  worst  meridian  of  the  other 
are  parallel,  one  image,  if  not  both,  of  every  object,  is  dis- 
placed on  the  retina.  If  one  image  of  an  object,  as  a  line, 
is  not  displaced  on  one  retina  and  the  other  image  is  dis- 
placed, they  fall  on  non-corresponding  parts  of  the  retinas, 
so  long  as  the  vertical  axes  remain  parallel  with  each  other. 
This  would  cause  diplopia.  If,  in  such  eyes,  both  images 
are  displaced,  they  cannot  fall  on  corresponding  retinal 
parts,  hence  there  would  be  diplopia,  if  the  vertical  axes 


COMPENSATING    HETEROTROPIA.  171 

remained  parallel.  Nature  has  made  provision  against  this 
diplopia. 

The  displacement  of  images  by  astigmatic  eyes  can  be 
best  understood  by  a  study  of  the  images  of  a  horizontal 
object,  as  an  arrow.  Figure  7  shows  the  two  images  on 
the  retinas  of  astigmatic  eyes  whose  meridians  of  greatest 
curvature  are  vertical.  (The  images  would  be  similarly 
related  if  the  eyes  were  non-astigmatic ;  and  the  same  would 
be  true  of  astigmatic  eyes  with  the  meridians  of  greatest 
curvature  horizontal.)  These  two  images  lie  on  corre- 
sponding meridians,  and,  therefore,  would  be  fused  without 
the  aid  of  any  basal  center,  the  eyes  being  orthophoric.  If 
the  arrow  were  held  in  any  oblique  position,  the  images 
would  fall  on  corresponding  parts  of  the  two  eyes,  for  the 
images  in  the  two  eyes  would  be  displaced  in  the  same  di- 
rection and  to  the  same  extent,  hence  would  be  fused  with- 
out the  aid  of  a  basal  center.  Since  the  fusion  faculty  of 
the  mind  acts  only  when  there  is  a  condition  that  would 
cause  diplopia,  this  faculty,  and  the  basal  centers  under  its 
control,  are  all  at  perfect  rest,  regardless  of  the  position,  in 
space,  of  the  object  of  fixation,  whenever  orthophoric  eyes 
have  equal  astigmatism,  the  meridians  of  greatest  curva- 
ture being  vertical.  The  same  is  true  of  astigmatic  eyes 
whose  meridians  of  greatest  curvature  are  horizontal. 

Figure  8  represents  a  pair  of  astigmatic  orthophoric 
eyes  in  which  the  meridian  of  greatest  curvature  in  each 


172 


COMPENSATING    HETEROTROPIA. 


eye  is  at  135°.  On  each  retina  the  image  of  the  arrow  is 
displaced  towards  the  meridian  of  greatest  curvature,  and 
to  the  same  extent.  As  shown  in  the  cut,  each  image  rests 
on  meridian  170°.  These  meridians  correspond,  therefore 
the  images  must  be  fused;  and  that,  too,  without  having 
caused  the  fusion  faculty  to  excite  a  single  basal  center. 
With  the  images  resting,  as  they  do,  on  retinal  meridians 


RIGHT 


LEFT 


Fig.  7. 


170°,  the  horizontal  arrow  will  appear  to  dip  10°  to  the 
left;  for  the  only  line  that  can  appear  to  be  horizontal  is 
the  one  whose  images  rest  on  meridians  180°,  when  the 
head  is  erect.  That  the  eyes  shown  in  Figure  8  may  see 
a  line  as  if  horizontal,  the  line  itself  would  have  to  be  in- 
clined 10°  to  the  right.  No  brain  center  need  act  in  the 
interest  of  fusion,  for  there  is  no  condition  to  cause  di- 
plopia ;  but  correct  orientation  with  such  eyes  is  impossible. 


COMPENSATING    HETEROTROPIA. 


173 


A  correction  of  this  symmetric  oblique  astigmatism  re- 
lieves no  basal  center,  for  none  has  been  active;  but  the 
correcting  lenses  so  change  the  images  that  a  horizontal  line 
has  horizontal  images;  a  vertical  line,  vertical  images;  and 
an  oblique  line,  images  of  the  same  obliquity.  The  cor- 
rection of  symmetric  oblique  astigmatism  is  largely  in  the 
interest  of  sharp  vision  and  correct  orientation ;  but,  as  will 


LEFT 


Fig.  8. 


be  shown  later,  such  correction  relieves  brain  centers  con- 
nected with  the  ciliary  muscles. 

Figure  9  represents  a  pair  of  astigmatic  orthophoric  eyes, 
the  meridian  of  greatest  curvature  of  the  left  eye  being 
vertical  and  that  of  the  right  eye  at  135°.  The  image  of 
the  horizontal  arrow,  in  the  left  eye,  will  lie  on  meridian 
180° ;  but  the  image  in  the  other  eye,  being  displaced 
towards  the  meridian  of  the  greatest  curvature,  will  lie  on 


174 


COMPENSATING   HETEROTROPIA. 


meridian  170°.  Since  these  two  meridians  do  not  corre- 
spond, there  would  be  diplopia,  if  the  vertical  axes  were 
allowed  to  remain  parallel.  To  prevent  the  diplopia,  the 
fusion  faculty  would  cause  the  right  sixth  basal  center  to 
send  neuricity  to  the  right  superior  oblique,  so  that  me- 
ridian 180°  shall  be  brought  under  the  displaced  image. 
The  fusion  is  effected  by  allowing  the  vertical  axis  of  the 


RIGHT 


LEFT 


Fig.  9. 


left  eye  to  remain  parallel  with  the  median  plane  of  the 
head,  while  the  vertical  axis  of  the  right  has  been  inclined 
10°  towards  the  median  plane,  this  inclination  being  ac- 
complished by  contraction  of  the  right  superior  oblique, 
under  the  stimulus  of  neuricity  sent  to  it  by  the  right  sixth 
basal  center.  Correction  of  the  astigmatism,  by  the  proper 
cylinders,  will  make  these  eyes,  to  all  intents  and  purposes, 
emmetropic,  hence  the  two  images  of  every  external  object 


COMPENSATING    HETEROTROPIA. 


175 


would  fall  on  corresponding  retinal  parts,  thus  putting  at 
rest  the  fusion  faculty,  the  right  sixth  basal  center  and 
the  right  superior  oblique  muscle. 

Figure  10  represents  a  pair  of  astigmatic  orthophoric 
eyes,  the  meridian  of  greatest  curvature  of  the  left  being 
at  90°  and  that  of  the  right  at  45°.  The  image  of  the 
horizontal  arrow,  in  the  left  eye,  lies  on  meridian  180°; 


PIGHT 


LEFT 


Fig. 


but  the  image  in  the  right  eye  has  been  displaced  so  that 
it  lies  on  meridian  10°.  Since  these  meridians  do  not  cor- 
respond, there  must  be  diplopia,  unless  the  fusion  faculty, 
through  the  proper  basal  center  and  muscle,  counteracts  it. 
The  fusion  faculty,  this  time,  causes  the  right  seventh  basal 
center  to  send  neuricity  to  the  right  inferior  oblique,  the 
contraction  of  which  so  torts  the  eye  as  to  bring  meridian 
180°  under  the  displaced  image.     In  effecting  fusion,  the 


176 


COMPENSATING    HETEROTROPIA. 


vertical  axis  of  the  left  eye  has  been  allowed  to  remain 
parallel  with  the  median  plane  of  the  head,  while  the 
vertical  axis  of  the  right  eye  has  been  inclined  10°  from 
this  plane.  A  correction  of  the  astigmatism  harmonizes 
images,  and  allows  the  fusion  faculty,  the  right  seventh 
basal  center,  and  the  inferior  oblique,  to  lapse  into  restful- 


RI6HT" 


LEFT 


Fig. 


Figure  11  represents  a  pair  of  astigmatic  orthophoric 
eyes,  the  meridian  of  greatest  curvature  of  the  right  eye 
being  at  135°  and  that  of  the  left  at  45°.  Both  images 
of  the  horizontal  arrow  are  displaced  and  in  opposite  direc- 
tions, but  in  obedience  to  the  same  law.  The  image,  in  the 
right  eye,  lies  on  meridian  175°,  and  that  in  the  left  eye 
on  meridian  5°.  These  two  meridians  do  not  correspond, 
hence  there  must  be  diplopia,  if  the  vertical  axes  are  allowed 


COMPENSATING    HETEROTROPIA. 


177 


to  remain  parallel.  Plate  XXXVI.  shows  how  the  fusion 
faculty  causes  the  right  and  left  sixth  basal  centers  to  send 
neuricity  to  the  two  superior  obliques,  so  that  they  may  tort 
the  two  eyes,  and  thus  bring  the  two  horizontal  meridians 
under  the  displaced  images.  The  vertical  axis  of  each  eye 
has  been  made  to  incline  5°  towards  the  median  plane  of 
the  head,  but  this  torting,  or  compensating  cyclotropia,  has 


RIOHT 


LEFT 


Fig.    12. 


prevented  diplopia.  If  the  compensating  cyclotropia  must 
be  the  same  in  each  eye,  it  could  be  effected  by  a  discharge 
of  neuricity  from  the  sixth  conjugate  center,  and  if  so, 
Plate  XXVIII.  would  show  the  brain  and  muscle  activity 
that  would  effect  it.  It  is  probably  true  that  the  sixth  con- 
jugate center  acts  only  with  the  second  conjugate  center, 
to  prevent  a  plus  cyclotropia  rather  than  cause  a  compen- 
sating minus  cyclotropia.    A  correction  of  the  astigmatism 


178 


COMPENSATING   HETEROTROPIA. 

?     i  12 


COMPENSATING    HETEROTROPIA. 


179 


180  COMPENSATING    HETEROTROPIA. 

will  harmonize  all  images,  and  thus  allow  the  fusion  faculty, 
the  right  and  left  sixth  basal  centers,  and  the  two  superior 
obliques,  to  assume  the  restful  state  normal  to  each. 

Figure  12  represents  a  pair  of  astigmatic  orthophoric 
eyes,  the  meridian  of  greatest  curvature  of  the  right  at 
45°,  and  that  of  the  left  at  135°.  The  image  of  the  hori- 
zontal arrow  in  the  right  eye  is  on  meridian  5°,  and  that 
in  the  left  eye  on  meridian  175°.  These  meridians  do  not 
correspond,  hence  there  must  be  diplopia,  if  the  vertical 
axes  are  allowed  to  remain  parallel.  The  prevent  the  diplo- 
pia, the  fusion  faculty  causes  the  right  and  left  seventh 
basal  centers  to  send  neuricity  to  the  two  inferior  obliques. 
These  muscles,  responding  to  the  stimulus  received,  tort  the 
two  eyes  out-ward,  so  that  the  normally  horizontal  meridian 
of  each  eye  may  be  brought  under  the  displaced  image,  and 
thus  make  fusion  possible.  This  action  of  basal  centers 
and  muscles  is  illustrated  in  Plate  XXXVII. 

Since  the  displacement  of  the  images  is  equal  in  the  two 
eyes  shown  in  Fig.  12,  it  would  be  possible  for  fusion  to 
be  effected  by  neuricity  sent  from  the  seventh  conjugate 
center,  provided  this  center  ever  acts  independently  of  the 
first  conjugat  center.  Such  activity  of  this  center,  if  it 
were  possible  for  it  to  effect  a  compensating  plus  cyclo- 
tropia,  would  be  illustrated  in  Plate  XXX.  If  it  is  not 
capable  of  producing  a  plus  cyclotropia,  it  cannot  coun- 
teract a  minus  cyclophoria,  hence  Plate  XXX.  would  have 


COMPENSATING    HETEROTROPIA.  181 

to  be  substituted  by  Plate  XXXVII.  Since  the  seventh 
conjugate  center  could  not  cause  the  inferior  obliques  to 
fuse  the  two  images,  whenever  one  image  is  more  displaced 
than  the  other,  though  in  opposite  directions,  it  is  reasonable 
to  conclude  that  this  center  never  undertakes  such  work, 
leaving  the  fusion  of  such  images  entirely  to  the  right  and 
left  seventh  basal  centers. 

Symmetric  astigmatism  means  astigmatism  equal  in  the 
two  eyes,  with  the  meridians  of  greatest  curvature  parallel ; 
non-symmetric  astigmatism  means  unequal  astigmatism  in 
the  two,  or  that  the  meridians  of  greatest  curvature  are  not 
at  the  same  angle ;  or  it  means  both  of  these. 

So  far  this  study  has  shown  that  symmetric  astigmatism 
does  not  call  on  the  fusion  faculty  to  excite  any  one  of  the 
four  basal  centers,  connected  with  the  oblique  muscles,  into 
fusional  activity;  that  non-symmetric  oblique  astigmatism 
always  makes  demands  on  one  or  two  of  the  four  basal  cen- 
ters connected  with  the  obliques ;  and  that  the  two  kinds  of 
astigmatism  differ  only  in  that  the  former  makes  no  de- 
mands on  either  of  the  four  fusional  centers  connected  with 
the  obliques,  while  the  latter  keeps  one,  if  not  two,  of  these 
centers  constantly  at  work  in  the  interest  of  fusion.  For 
lack  of  a  better  name,  this  work  has  been  called  compensat- 
ing cyclotropia. 

Plates  XXXVIII.  and  XXXIX.  are  introduced  here  to  im- 
press still  further  the  image  changes  caused  by  non-sym- 


134  COMPENSATING   HETEROTROPIA. 

metric  oblique  astigmatism ;  and,  to  illustrate  the  torsioning 
that  must  take  place,  in  the  latter,  in  order  that  there  may 
be  fusion,  though  imperfect.  Another  important  lesson  that 
Plate  XXXIX.  teaches  is  that,  when  both  vertical  and  hori- 
zontal lines  compose  a  figure  (the  rectangle)  the  mind  ef- 
fects, by  preference,  the  fusion  of  the  horizontal  lines. 
This  may  have  some  relationship  with  the  fact  that  the 
fusion  field  of  the  retina  is  greater  horizontally  than  verti- 
cally. 

Plate  XXXVIII.  represents  a  pair  of  symmetric  astig- 
matic eyes,  the  meridians  of  greatest  curvature  being  either 
vertical  or  horizontal.  The  object  of  view  is  a  rectangle, 
the  upper  and  lower  borders  being  horizontal,  and  in  each 
eye  the  image  is  also  a  rectangle.  Either  eye  alone,  or 
the  two  together,  would  see  the  figure  as  it  is,  a  rectangle. 
Looking  closely  at  the  image  it  will  be  seen  that  the  upper 
and  lower  borders  of  the  images,  corresponding,  respective- 
ly, with  the  lower  and  upper  borders  of  the  figure,  are 
parallel  with  the  horizontal  retinal  meridians;  and  that  the 
right  and  left  borders  of  the  images,  corresponding  respect- 
ively with  the  left  and  right  borders  of  the  figure,  are  par- 
allel with  the  vertical  retinal  meridians.  The  lines  con- 
necting parts  of  the  images  and  the  object  that  correspond, 
represent  lines  of  direction,  all  of  which  cross  at  a  common 
point,  the  center  of  retinal  curvature;  for  each  line  of  di- 
rection, in  eyes  whose  vertical  axes  are  parallel  with  the 


COMPENSATING    HETEROTROPIA.  185 

median  plane  of  the  head,  is  a  radius  of  retinal  curvature 
prolonged.  Each  eye  sees  the  rectangle  as  it  is  and  where 
it  is.  That  these  eyes  have  not  been  torted,  in  the  interest 
of  fusion,  is  shown  by  the  fact  that  the  two  horizontal 
meridians  lie  in  a  common  plane,  and  the  two  vertical 
meridians  are  perfectly  parallel. 

If  the  rectangular  figure  were  held  obliquely  in  front  of 
these  eyes,  the  two  images  would  be  alike,  but  each  would 
be  a  non-rectangular  parallelogram.  All  the  lines  of  di- 
rection would  cross  at  a  common  point,  and  each  two  lines 
would  intersect  at  a  common  corner  of  the  figure,  but  the 
lines  forming  the  figure  would  not  make  it  apepar  as  a  rec- 
tangle, but  as  a  non-rectangualar  parallelogram.  Confin- 
ing to  rotate  the  rectangular  figure,  the  images  as  continually 
change  in  shape,  until,  the  sides  becoming  vertical  and  the 
ends  horizontal,  the  images  are  again  rectangular,  and  the 
figure  is  seen  once  more  as  a  rectangle.  Whatever  may  be 
the  position  of  the  figure  before  these  eyes,  and  however  it 
may  appear  distorted,  the  fusion  has  been  effected  without 
excitation  of  a  single  basal  center,  or  the  contraction  of  a 
single  muscle. 

The  same  rectangle  held  before  non-astigmatic  eyes,  in 
any  position,  would  have  formed  on  each  retina  a  rectan- 
gular image,  and  the  figure  in  all  positions  would  appear  as 
a  rectangle.  A  correction  of  the  astigmatism  makes  the 
eyes,  shown  in  Plate  XXXVIII.,  emmetropic;  and  the  rec- 


186  COMPENSATING    HETEROTROPIA. 

tangular  figure,  held  in  an  oblique  position,  would  be  seen 
as  a  perfect  rectangle,  just  as  perfect  as  the  one  shown  in 
the  plate.  There  would  be  no  metamorphosia  to  annoy  the 
wearer  of  the  correcting  lenses.  Metamorphopsia  is  not 
caused  by  the  wearing  of  cylinders  that  correct  symmetric 
astigmatism,  whether  the  meridians  of  greatest  curvature 
are  vertical,  horizontal  or  oblique.  The  reason  for  the  ab- 
sence of  the  metamorphopsia,  in  these  cases,  is:  Not  one 
of  the  four  basal  centers,  connected  with  the  four  obliques, 
has  ever  been  excited  in  the  interest  of  fusion,  hence  not 
one  of  these  centers  has  formed  a  habit  that  it  will  take 
time  to  break.  In  monocular  vision,  basal  centers  that  have 
been  active  in  binocular  vision,  lapse  at  once  into  a  state 
of  rest;  but  an  attempt  to  use  the  two  eyes  at  once  arouses 
these  centers  into  action.  The  condition  demanding  ac- 
tivity of  these  centers  may  have  been  removed,  but,  not- 
withstanding, the  old  habit  of  action  will  assert  itself  for 
a  time.  This  will  be  better  understood  in  the  study  of  the 
next  plate. 

Plate  XXXIX.  represents  a  pair  of  non-symmetric  astig- 
matic eyes,  the  meridian  of  greatest  curvature  of  the  right 
eye  at  135°  and  that  of  the  left  eye  at  45°.  The  same  rec- 
tangular figure  is  held  before  these  eyes  as  was  held  before 
the  symmetric  astigmatic  eyes  shown  in  Plate  XXXVIII. 
In  Plate  XXXIX.  there  is,  on  each  retina,  a  distorted  image 
— a   non-rectangular  parrallelogram   image — and  the   dis- 


COMPENSATING    HETEROTROPIA.  187 

tortion  is  in  opposite  directions.  With  either  eye  alone,  the 
rectangle  will  appear  to  be  a  non-rectangular  parallelogram. 
The  one  seen  by  the  right  eye  would  lean  down  to  the  left ; 
and  the  one  seen  by  the  left  eye  would  lean  down  to  the 
right.  To  fuse  such  images  even  imperfectly,  the  fusion 
faculty  of  the  mind  must  cause  the  right  and  left  six  basal 
centers  to  send  neuricity  to  their  respective  superior 
obliques.  These  muscles  responding  cause  a  compensating 
minus  cyclotropia,  and  the  fusion  of  the  two  images  results 
not  in  showing  the  figure  as  a  rectangle  nor  as  a  non-rec- 
tangular parallelogram,  but  as  a  trapezoid,  abed'.  The 
cyclotropia  of  the  right  eye  has  brought  the  upper  and 
lower  borders  of  the  figure  seen  by  it  into  the  horizontal, 
but  the  two  ends  are  not  vertical,  though  parallel.  This 
figure,  which  is  a  part  of  the  fused  figure,  is  a,  b,  c,  d. 
The  cyclotropia  of  the  left  eye  has  placed  the  horizontal 
meridian  parallel  with  the  upper  and  lower  borders  of  the 
image,  but  the  ends  are  further  from  being  parallel  with  the 
now  inclined  vertical  meridian.  The  figure  seen,  which  is 
a  part  of  the  fused  figure,  is  a'  b  c  d' .  The  plate  shows 
a  perfect  fusion  of  the  lower  border  of  the  figure,  an  in- 
complete fusion  of  the  upper  border,  but  no  fusion  at  all 
of  the  ends.  The  imperfect  fusion  of  the  two  non-rectan- 
gular parallelograms  develops  the  perfect  trapezoid,  the 
very  best  that  such  eyes  can  do  in  the  way  of  fusion  of  the 
dissimular  images.     The  plate  shows  that  the  two  superior 


188  COMPENSATING    HETEROTROPIA. 

obliques  have  made  the  two  horizontal  meridians  dip  down 
and  in,  and  have  made  the  two  vertical  meridians  incline 
towards  each  other.  The  dipping  horizontal  meridian  in 
each  eye  is  thus  made  parallel  with  the  upper  and  lower 
borders  of  the  distorted  image,  hence  the  corresponding 
borders  of  the  figure  appear  horizontal.  The  vertical  me- 
ridian, however,  is  not  so  nearly  parallel  with  the  two  ends 
of  the  image  as  it  was  before  torsioning  occurred,  hence  the 
two  ends  of  the  fused  object  are  far  from  being  vertical. 
The  right  border  of  the  fused  object  is  seen  by  the  right 
eye  only,  and  is  inclined  from  the  median  plane  of  the  head ; 
the  left  border  of  the  fused  object  is  seen  by  the  left  eye 
only,  and  is  inclined  from  the  median  plane.  Thus  the 
trapezoid  has  its  longer  side  at  the  top. 

The  trapezoid  would  be  inverted  if  it  were  seen  by  non- 
symmetric  astigmatic  eyes,  whose  meridians  of  greatest 
curvature  converge  above — that  of  the  right  being  at  45°, 
and  that  of  the  left  at  135°.  The  distorted  images  in  such 
eyes  would  be  fused  by  the  action  of  the  right  and  left  sev- 
enth basal  centers  on  the  inferior  obliques,  as  illustrated 
in  Plate  XXXVII.  In  each  of  these  eyes  the  parallelogram 
image  would  dip  down  and  out,  and  the  plus  cyclotropia 
would  make  the  horizontal  meridian  dip  down  and  out  just 
enough  to  make  it  parallel  with  the  upper  and  lower  bor- 
ders of  the  image.      This  compensating  plus   cyclotropia 


COMPENSATING    HETEROTROPIA.  189 

would  make  a  rectangle  appear  to  be  a  trapezoid  with  the 
longer  side  below. 

Referring  again  to  Plate  XXXIX,,  the  result  of  the  cor- 
rection of  the  astigmatism  would  be  the  correction  of  the 
distortion  of  the  image  in  each  eye ;  that  is  to  say,  the  rec- 
tangular object  would  have  a  rectangular  image,  the  upper 
and  lower  borders  of  the  image  being  parallel  with  the 
horizontal  meridian,  and  the  end  borders  would  be  parallel 
with  the  vertical  meridian.  With  the  one  eye  covered,  the 
other  eye  would  see  the  figure  as  it  is — a  rectangle,  and 
in  its  true  position ;  for  in  monocular  vision,  with  or  with- 
out the  correcting  cylinder  on,  the  sixth  basal  center,  for 
that  eye,  will  become  quiet,  thus  allowing  the  vertical  axis 
of  the  eye  to  become  parallel  with  the  median  plane  of  the 
head.  This  would  be  true  of  either  eye  alone.  But  the 
moment  that  binocular  vision,  through  the  correcting  cyl- 
inders, is  attempted,  the  right  and  left  sixth  basal  centers, 
from  long  habit,  will  send  neuricity  to  the  superior  obliques. 
The  result  will  be  to  make  the  rectangular  figure  appear  as 
a  trapezoid,  the  longer  side  being  below.  From  infancy  the 
patient  has  been  accustomed  to  the  trapezoid  shape  of  a 
rectangle,  the  longer  side  above,  and  may  not  be  able  to 
detect  it  when  questioned  as  to  its  shape ;  but  when,  because 
of  a  continuance  of  the  fusional  activity  of  the  two  sixth 
basal  centers,  the  correcting  cylinders  are  made  to  distort 
the  rectangle  into  a  trapezoid,  longer  side  below,  the  change 


190  COMPENSATING    HETEROTROPIA. 

is  observed  at  once.  The  opposite  wall  of  a  room  will 
appear  to  lean  from  him,  and  the  floor  will  appear  to  slant 
towards  him.  These  changes  are  more  or  less  annoying  to 
all  patients  unless  they  are  told  about  them  beforehand. 
When  the  eyes  are  like  those  in  Plate  XXXIX.,  the  patient 
can  be  assured,  nearly  always,  that  these  annoyances  will 
disappear  within  two  or  three  days.  It  is  a  matter  of  ob- 
servation that  the  habit  of  fusional  activity  of  the  right 
and  left  sixth  basal  centers  and  of  the  two  superior  obliques 
is  soon  given  up,  when  the  necessity  for  it  has  been  re- 
moved; and  the  moment  the  habit  is  broken  a  rectangle 
appears  as  a  rectangle,  the  floor  becomes  level  and  the  wall 
becomes  vertical.  After  having  become  accustomed  to  the 
normal  condition  of  external  objects,  as  seen  through  cor- 
recting cylinders,  on  removing  the  lenses  the  patient  will 
say  that  a  rectangle  is  longer  at  the  top  than  at  the  bottom, 
that  the  floor  slants  from  him,  and  that  the  wall  leans 
towards  him. 

The  correcting  cylinders  of  astigmatic  eyes,  whose  me- 
ridians of  greatest  curvature  converge  above,  are  more 
annoying,  and  for  a  longer  time,  than  when  these  meridians 
diverge  above.  The  only  explanation,  as  to  the  longer 
duration  of  the  metamorphopsia,  is  that  the  right  and  left 
seventh  basal  centers,  and  the  strong  inferior  obliques,  are 
slow  to  give  up  their  habit  of  fusional  activity,  even  after 
the  necessity  for  such  activity  has  ben  removed.     Even  in 


COMPENSATING    HETEROTROPIA.  191 

these  cases,  if  the  axes  of  the  cylinders  have  been  carfully 
and  correctly  placed,  the  patient  can  be  assured  that,  in  a 
week  or  two,  a  rectangle  will  cease  to  appear  longer  at  the 
top ;  that  the  floor  will  continue  to  rise  at  the  wall,  until  it 
becomes  level;  and  that  the  wall,  at  the  floor,  will  continue 
to  approach  him  until  it  becomes  perfectly  vertical. 

Again,  it  may  be  said  that  the  correcting  cylinders  of 
symmetric  oblique  astigmatism  never  causes  metamorphop- 
sia,  nor  does  the  correction  of  vertical  and  horizontal  astig- 
matism cause  it,  and  for  the  simple  reason  that  neither  the 
right  and  left  sixth,  nor  the  right  and  left  seventh,  basal 
centers  have  ever  been  excited,  by  these  conditions,  into 
fusional  activity,  hence  they  never  have  formed  a  habit  that 
must  be  broken.  Both  with  and  without  the  correcting 
cylinders,  the  obliques  of  such  eyes  simply  maintain  paral- 
lelism between  their  vertical  axes  and  the  median  plane  of 
the  head,  and,  if  orthophoric,  they  do  this  without  activity 
of  a  single  basal  center. 

There  is  work  done  by  nerve  centers  and  by  the  two 
muscles  in  the  ciliary  body,  common  to  all  forms  of  hy- 
peropic  astigmatism — both  the  symmetric  and  the  non-sym- 
metric— in  both  distant  and  near  vision;  also  common  to 
all  forms  of  low  myopic  astigmatism,  in  near  work.  The 
Muller  muscles  and  the  conjugate  center  (the  tenth)  con- 
trolling them,  are  active,  doubtless ;  but  the  best  they  can  do 
is  to  relate  the  two  foci,  to  the  rectina,  so  that  the  one  shall 


192  COMPENSATING   HETEROTROPIA. 

be  just  as  far  in  front  of  it  as  the  other  is  behind  it.  In 
unequal  astigmatism,  one  of  the  tenth  basal  centers,  doubt- 
less, is  active  also. 

That  another  natural  provision  has  been  made  for 
the  correction,  in  part  or  wholly,  of  astigmatism  would 
appear  from  the  anatomic  nature  of  Bowman's  muscle  in 
the  ciliary  body.  If  the  fibers  of  this  muscle,  running 
meridionally,  effect  any  change  in  the  power  of  the  lens, 
it  must  be  by  tilting  it.  It  is  well  known  that  tilting  a 
lens  increases  its  power  at  right  angles  to  the  axis  of  the 
rotation.  Since  the  aim  of  the  lenticular  astigmatism,  thus 
produced,  must  be  the  correction  of  a  corneal  astigmatism, 
the  axis  of  the  lens  rotation  must  lie  in  a  plane  with  the 
meridian  of  greatest  corneal  curvature.  The  rotation 
power  must  reside  in  the  Bowman  muscle;  the  contracting 
fibers  must  be  in  a  single  part  of  that  muscle,  and  this  part 
must  be  situated  on  only  one  side  of  the  plane  of  the  axis 
of  rotation,  and  just  90°  from  it.  It  could  be  on  either 
side.  The  anatomic  arrangement  of  the  fibers  of  Bowman's 
muscle  is  such  that  physiologic  activity  might  be  excited 
in  one  part  while  all  other  parts  are  at  rest.  This  muscle 
is  presided  over,  probably,  by  the  superior  cervical  sympa- 
thetic, as  are  the  radiating  fibers  of  the  iris.  However  this 
may  be,  it  is  certain  that  the  nerve  endings,  controlling 
Bowman's  muscle,  cannot  be  influenced  by  atropia  or  any 
other  known  drug.     Hence  it  is  impossible,  in  many  cases, 


COMPENSATING    HETEROTROPIA.  193 

to  uncover  all  the  corneal  astigmatism  with  any  agent  that 
will  put  at  rest  the  Muller  muscle.  In  time,  the  power  of 
the  Bowman  muscle  wanes,  as  does  that  of  the  Muller  mus- 
cle, and  then  the  full  amount  of  corneal  astigmatism  be- 
comes manifest. 

In  adjusting  astigmatic  lenses,  there  is  no  excuse  for  not 
suspending  the  power  of  the  Muller  muscle,  and  thus  make 
the  eye  show  whether  the  astigmatism  is  mixed  or  hyper- 
opia notwithstanding  the  fact  that  no  known  drug  can 
suspend  the  neutralizing  lenticular  astigmatism.  A  full 
correction  of  manifest  astigmatism,  under  a  mydriatic,  leads 
to  a  further  manifestation  of  corneal  astigmatism.  In- 
creasing the  strength  of  the  cylinder,  as  more  of  the  real 
error  is  thus  teased  from  under  cover,  in  a  few  years  the 
whole  error  becomes  manifest,  and  then  the  full  corection 
of  the  corneal  astigmatism  should  be  given.  Future  ex- 
perience must  settle  the  question :  "Would  it  be  well  to  fully 
correct  the  astigmatism  shown  by  the  ophthalmometer,  al- 
though, temporarily,  the  patient's  vision  might  be  made 
less  acute?"  Astigmatism  per  se  may  be  corrected  by 
either  +  or  —  cylinders,  but  the  kind  of  cylinder  to  be 
given,  and  whether  or  not  it  shall  be  associated  with  a 
sphere,  can  be  determined  accurately  only  when  the  eyes 
are  under  the  influence  of  a  mydriatic.  The  mydriatic  does 
not  change  the  distance  between  the  two  foci  (only  the  two 
principal  meridians  have  foci),  but  it  fixes  accurately  the 


194  COMPENSATING   HETEROTROPIA. 

static  relationship  that  the  anterior  focus  bears  to  the 
retina.  Bowman's  muscle  influences  the  posterior  focus 
only.  With  the  anterior  focus  located  where  static  refrac- 
tion would  place  it,  the  astigmatic  error  can  be  corrected 
intelligently;  otherwise,  any  effort  at  correction  is  only 
guess-work. 

A  full  correction  of  corneal  astigmatism  relieves  the 
tenth  conjugate  center  and  Muller's  muscles  from  abnormal 
work ;  it  also  brings  rest  to  Bowman's  muscle  and  to  the  cen- 
ter controlling  it,  which  is,  probably,  the  superior  cervical 
sympathetic  ganglion,  or  a  still  higher  center  with  which 
it  may  be  connected.  This  is  the  whole  relief  that  comes 
from  the  correction  of  symmetric  astigmatism;  and  this 
relief  would  come,  to  such  eyes,  as  the  result  of  advancing 
years,  if  no  lenses  were  ever  given.  Lenses  cut  short  the 
suffering  that  is  caused  by  abnormal  work  of  the  centers 
and  muscles  mentioned,  and  also  bring  pleasure  by  sharp- 
ening vision. 

There  are  brain  centers  and  muscles  that  must  act  in 
uncorrected  non-symmetric  oblique  astigmatism,  to  which 
no  rest  can  come  because  of  advancing  years.  These  cen- 
ters are  the  right  and  left  sixth,  and  right  and  left  seventh, 
basal  centers,  and  the  muscles  are  the  superior  and  inferior 
obliques.  Correcting  cylinders  alone  can  relieve  the  oblique 
muscles  and  the  basal  centers  connected  with  them.  With- 
out correcting  cylinders,  the  suffering  of  those  who  have 


COMPENSATING    HETEROTROPIA.  195 

oblique  astigmatism  is  commensurate  with  the  duration  of 
life. 

If  it  is  important  to  correct  symmetric  oblique  astigma- 
tism, and  vertical  or  horizontal  astigmatism,  it  must  appear 
doubly  important  to  correct  non-symmetric  oblique  astigma- 
tism. 

Metamorphopsia. 

The  metamorphopsia  caused  by  the  wearing  of  fully  cor- 
recting plus  cylinders,  when  the  axes  are  in  the  upper  tem- 
poral quadrants,  or  minus  cylinders  with  axes  in  upper 
nasal  quadrants,  is  so  transient,  in  most  cases,  that  noth- 
ing need  to  be  done  to  modify  it.  Occasionally,  however, 
such  a  patient  is  so  much  annoyed  something  must  be  done 
other  than  making  the  declaration  that  these  troubles  will 
pass  away,  under  the  persistent  wearing  of  the  lenses. 

The  metamorphopsia  is  so  prolonged  and  disagreeable, 
when  the  axes  of  plus  cylinders  are  in  the  upper  nasal  quad- 
rants, or  when  the  axes  of  minus  cylinders  are  in  the  upper 
temporal  quadrants,  something  must  be  done  to  modify  it. 
Otherwise  many  patients  would  discard  their  lenses.  There 
are  two  methods  of  procedure,  either  one  of  which  may  be 
adopted  successfully.  One  is  the  Lippincott  method,  which 
is  to  give  only  a  partial  correction  (about  one-third)  of 
the  manifest  astigmatism,  at  the  beginning.  This  causes 
but  slight  metamorphopsia,  which  soon  vanishes;  and  then 


196  COMPENSATING   HETEROTROPIA. 

still  stronger  cylinders,  a  two-thirds  correction,  are  given. 
The  slight  metamorphopsia  caused  by  the  new  lenses  soon 
disappears.  Now  the  full  strength  cylinders  may  be  given, 
with  a  resulting  metamorphopsia  both  slight  and  transient. 
By  this  method  the  breaking  of  the  habit  of  brain  centers 
and  muscles  is  easily  accomplished,  and  with  but  little  an- 
noyance to  the  patient.  This  method  is  not  often  applicable 
to  astigmatism  in  which  the  meridians  of  greatest  curvature 
are  in  the  upper  temporal  quadrants. 

The  other  method  is  the  shifting  of  the  axes  of  the  cor- 
recting cylinders,  in  the  direction  of  the  continued  torsion- 
ing,  sufficiently  far  to  make  the  slanting  floor  almost  level. 
At  intervals  of  two  or  three  days  the  axes  should  be  moved 
slightly  towards  the  degree  mark  selected  in  the  monocular 
tests,  which  point  should  be  reached  at  the  third  or  fourth 
backward  shifting.  By  this  method  the  habit  of  brain  cen- 
ters and  muscles  is  as  easily  broken  as  by  the  Lippincott 
method.  The  cost  of  changing  lenses  two  or  three  times  is 
the  only  objection  to  the  giving  of  partial  corrections,  in 
suitable  cases. 

The  following  simple  rule  may  be  given  for  the  shifting 
of  both  plus  and  minus  cylinders  for  lessening  metamor- 
phopsia: The  axes  of  plus  cylinders,  whether  in  the  upper 
temporal  or  upper  nasal  quadrants,  should  be  shifted  to- 
ivards  their  respective  verticals;  the  axes  of  minus  cylin- 
ders, whether  in  the  upper  nasal  or  upper  temporal  quad- 


COMPENSATING    HETEROTROPIA.  197 

rants,  should  be  shifted  towards  their  respective  horizon- 
tals.  The  shifting  should  be  only  so  far  as  to  almost  level 
the  floor;  and  by  degrees,  these  axes  should  be  returned  to 
the  points  on  the  arcs  determined  for  them,  by  both  ophthal- 
mometer and  trial  lenses,  in  the  monocular  tests. 

For  emphasis  it  may  be  stated  again  that,  for  lessening 
metamorphopsia,  plus  cylinders  will  require  shifting  rarely, 
if  their  axes  are  located  in  the  upper  temporal  quadrants ; 
and  that  minus  cylinders,  with  their  axes  in  the  upper  nasal 
quadrants,  will  need  shifting  just  as  infrequently.  In  either 
case  the  right  and  left  sixth  basal  centers  and  the  two  su- 
perior oblique  muscles  learn  speedily  to  suspend  their 
efforts  to  maintain  the  minus  cyclotropia  formerly  re- 
quired by  the  fusion  faculty.  Astigmatics,  who  have  been 
punished  by  the  necessity  for  compensating  minus  cyclo- 
tropia, nearly  always  enjoy  their  correcting  cylinders  from 
the  beginning. 

The  astigmatic  condition  requiring  that  the  axes  of  plus 
cylinders  shall  be  in  the  upper  nasal  arcs,  or  that  the  axes 
of  minus  cylinders  shall  be  in  the  upper  temporal  arcs,  when 
uncorrected,  made  it  necessary  for  the  right  and  left  sev- 
enth basal  centers  to  force  the  inferior  obliques  into  fu- 
sional  activity.  Because  these  centers  and  muscles  are  slow 
to  give  up  their  work  of  cyclo-duction,  even  after  the  need 
for  it  no  longer  exists,  the  axes  of  the  cylinders  should  be 
shifted  according  to  the  rule  given  above,  the  only  purpose 


198  COMPENSATING    HETEROTOPIA. 

of  the  shifting  being  to  lessen  the  metamorphopsia,  and 
minimize  the  annoyances  while  the  habit  is  being  broken. 

Artificial  Causes  of  Compensating  Heterotropia. 

Prisms. — A  prism  placed  base  out  before  an  eye  de- 
mands that  there  shall  be  a  compensating  esotropia,  other- 
wise there  would  be  diplopia.  If  the  eye  is  esophoric,  the 
excessive  tonicity  of  the  internus  may  turn  it  in  sufficiently 
to  effect  fusion.  If  so,  the  prism  thus  placed,  instead  of 
exciting  the  third  basal  center  and  causing  the  internus 
to  contract,  brings  rest  to  the  fourth  basal  center  and  the 
externus,  previously  at  work  to  counteract  the  esophoria. 
Before  such  an  eye  the  prism  would  do  good,  and  not  harm. 

The  same  prism,  similarly  placed  before  an  orthophoric 
eye,  would  excite  into  activity  the  third  basal  center,  which 
would  cause  the  internus  to  turn  the  eye  in,  by  its  contrac- 
tile power.  By  creating  a  necessity  for  fusional  activity 
of  a  basal  center  and  the  muscle  controlled  by  it,  the  prism 
would  be  a  bad  thing,  and  would  cause  suffering. 

The  same  prism,  similarly  placed  before  an  exophoric  eye, 
would  be  more  hurtful  still;  for  it  would  increase  the  de- 
mand on  the  third  basal  center  and  the  internus,  already 
engaged  in  the  work  of  counteracting  the  exophoria. 

A  prism,  base  out,  will  do  good  if  the  eye  is  esophoric, 
will  do  harm  if  the  eye  is  orthophoric,  will  do  greater  harm 


COMPENSATING    HETEROTROPIA.  199 

if  the  eye  is  exophoric.  In  all  three  instances  there  has 
been  developed  a  compensating  esotropia,  but  in  the  first 
instance  the  esotropia  was  effected  by  tonicity;  in  the  two 
other  instances  by  contractility,  effected  by  an  excited  basal 
center. 

For  the  same  reason,  a  prism,  base  in,  will  do  good  if  the 
eye  is  exophoric,  but  will  do  harm  if  the  eye  is  orthophoric 
or  esophoric. 

A  prism,  base  down,  will  help  a  hyperphoric  eye,  but  will 
be  harmful  to  an  orthophoric  or  a  cataphoric  eye. 

A  compensating  heterotopia  which  is  effected  by  muscle 
tonicity  is  a  good  thing;  but  a  compensating  heterotropia 
which  must  be  effected  by  brain  activity  and  muscle  con- 
traction is  a  bad  thing. 

The  compensating  heterotropia,  caused  by  either  natural 
or  artificial  conditions,  may  be  effected  by  muscle  tonicity, 
but  more  often  is  effected  by  muscle  contractility.  The 
compensating  heterotropia  effected  by  muscle  tonicity 
should  be  allowed  to  continue;  but  the  cause  of  a  compen- 
sating heterotropia  which  is  effected  by  brain  activity  and 
muscle  contraction  should  be  removed. 

One  of  the  most  common  and  hurtful  causes  of  compen- 
sating heterotropia  is  the  incorrect  wearing  of  lenses  which, 
in  themselves,  may  be  perfect.  Convex  lenses  for  either 
hyperopia  or  presbyopia,  and  concave  lenses  for  myopia, 
should  be  so  placed  before  eyes  as  not  to  excite  fusional 


200  COMPENSATING    HETEROTROPIA. 

activity  of  basal  centers  and  muscles;  and  if  such  activity 
exists  without  lenses  it  should  be  relieved  by  them,  if  pos- 
sible. 

If  eyes  are  orthophoric,  convex  or  concave  lenses  should 
be  in  frames  of  a  width  corresponding  to  the  distance  be- 
tween the  pupillary  centers,  and  should  be  perfectly  level. 
Thus  worn,  .no  basal  center  will  be  excited  nor  will  any 
muscle  be  made  to  do  abnormal  work.  Should  convex 
lenses  be  in  frames  that  are  too  wide,  or  concave  lenses 
be  in  frames  that  are  too  narrow,  the  right  and  left 
third  basal  centers,  and  the  interni,  must  be  continually 
active  in  the  production  of  compensating  esotropia.  Should 
convex  lenses  be  in  frames  that  are  too  narrow,  or  concave 
lenses  in  frames  that  are  too  wide,  the  right  and  left  fourth 
basal  centers  and  the  externi  must  be  continually  active  in 
the  production  of  compensating  exotropia.  When  specta- 
cles lean  to  the  right,  if  they  contain  convex  lenses,  the  right 
first  basal  center  and  its  superior  rectus  muscle  must  take 
on  fusional  activity,  and  the  left  second  basal  center  and 
its  inferior  rectus  must  become  active  also.  If  spectacles, 
leaning  to  the  right,  contain  concave  lenses,  the  right  second 
basal  center  and  its  inferior  rectus,  and  the  left  first  basal 
center  and  its  superior  rectus,  must  all  become  active  in 
the  interest  of  fusion. 

Only  in  e?ophoria  should  convex  lenses  be  wider  apart, 
and  concave  lenses  closer  together,  than  the  pupillary  meas- 


COMPENSATING    HETEROTROPIA.  201 

urement  calls  for,  the  justification  for  this  being  the  relief 
they  bring  to  the  right  and  left  fourth  basal  centers  and  the 
external  recti,  by  the  development  of  a  tonicity  compensat- 
ing esotropia. 

Only  in  exophoria  should  convex  lenses  be  closer  together 
and  concave  lenses  wider  apart  than  indicated  by  the  pupil- 
lary measurement,  and  for  the  reason  that,  thus  related, 
they  would  relieve  the  right  and  left  third  basal  centers,  and 
the  interni  from  fusional  activity. 

Convex  lenses  in  frames  inclined  to  the  right,  before 
orthophoric  eyes,  must  cause  diplopia,  unless  this  is  pre- 
vented by  activity  of  the  right  first  basal  center  and  its  su- 
perior rectus,  in  the  production  of  compensating  right  hy- 
pertropia,  and  of  the  left  second  basal  center  and  its  in- 
ferior rectus,  in  the  production  of  compensating  left  cata- 
tropia.  So  long  as  the  frames  are  thus  leaning,  these  cen- 
ters and  muscles,  which  ought  to  be  at  rest,  will  be  forced 
by  the  fusion  faculty  to  continue  this  abnormal  activity. 
Symptoms  of  some  character  must  arise,  for,  soon  or  late, 
these  centers  and  muscles  will  rebel,  and,  in  their  rebellion, 
will  have  the  sympathy  of  other  centers,  basal  or  cortical. 
The  remedy  is  the  leveling  of  the  lenses. 

If  a  patient  has  right  hyperphoria,  the  leaning  of  frames, 
containing  convex  lenses,  to  the  right  will  cause  a  tonicity 
compensating  right  hypertropia  and  left  catatropia,  which 
will  relieve  the  right  second  basal  center  and  its  inferior 


202  COMPENSATING   HETEROTROPIA. 

rectus,  and  the  left  first  basal  center  and  its  superior  rec- 
tus; but  the  leaning  of  the  frames  to  the  left  would  make 
the  lenses  unbearable,  by  compelling  the  centers  and  mus- 
cles named  to  do  additional  work. 

The  oculist  cannot  be  too  careful  in  adjusting  frames  that 
will  contain  lenses  he  may  have  prescribed;  nor  should  he 
be  remiss  in  his  duty  to  his  patients,  by  failing  to  impress 
them  with  the  importance  of  keeping  the  lenses  properly 
related  to  the  eyes. 

Cylindric  Lenses. — The  only  remaining  artificial  cause  of 
compensating  heterotropia  is  the  cylindric  lens.  Eyes  that 
are  not  astigmatic  can  be  made  so  by  either  convex  or 
concave  cylinders.  The  astigmatism  they  produce  is  sym- 
metric if  the  cylinders  are  of  the  same  kind,  equal  in 
strength  and  their  axes  are  parallel.  Otherwise,  the  arti- 
ficial astigmatism  would  be  non-symmetric.  In  symmetric 
artificial  astigmatism,  images  must  be  blurred  more  or  less, 
but  there  will  be  no  cause  for  compensating  cyclotropia, 
hence  there  would  be  no  activity  of  either  the  right  and 
left  sixth  basal  centers  and  their  superior  obliques,  or  of 
the  right  and  left  seventh  basal  centers,  and  their  inferior 
obliques. 

Artificial  astigmatism  produced  by  convex  cylinders 
whose  axes  are  in  the  upper  nasal  arcs,  or  by  concave  cylin- 
ders whose  axes  are  in  the  upper  temporal  arcs,  will  have 
images  so  distorted  as  to  produce  diplopia  which  can  be 


COMPENSATING    HETEROTROPIA.  203 

prevented  only  by  compensating  minus  cyclotropia.  This 
work  must  be  done  by  the  right  and  left  sixth  basal  centers 
acting  on  the  two  superior  obliques. 

In  artificial  astigmatism  produced  by  convex  cylinders 
whose  axes  are  in  the  upper  temporal  arcs,  or  by  concave 
cylinders  whose  axes  are  in  the  upper  nasal  arcs,  images 
will  be  so  distorted  as  to  call  into  fusional  activity  the  right 
and  left  seventh  basal  centers  and  the  inferior  obliques.  So 
long  as  the  cylinders,  thus  placed,  are  in  front  of  the  eyes, 
compensating  plus  cyclotropia  must  be  maintained.  Ortho- 
phoric  obliques,  and  their  centers,  cannot  endure  this  work, 
hence  such  lenses,  however  obtained,  would  be  cast  aside. 

Compensating  cyclotropia,  effected  by  tonicity  of  the 
obliques,  relieves,  rather  than  excites,  basal  centers;  hence 
the  production  of  artificial  non-symmetric  astigmatism  is 
justifiable  when  there  is  cyclophoria,  provided  other  treat- 
ment will  not  be  acepted.  In  plus  cyclophoria,  as  illustrated 
in  Plate  XXXVL,  the  right  and  left  sixth  basal  centers 
and  the  two  superior  obliques  are  acting  in  the  maintain- 
ance  of  parallelism  of  the  vertical  axes  of  the  eyes  with 
the  median  plane  of  the  head.  If  plus  cylinders,  with  their 
axes  in  the  upper  temporal  arcs,  or  minus  cylinders  with 
their  axes  in  the  upper  nasal  arcs,  are  placed  before  these 
eyes,  images  will  be  displaced  so  as  to  excite  compensating 
plus  cyclotropia.  This  would  be  effected  by  the  tonicity 
of  the  strong  inferior  obliques ;  and  the  right  and  left  sixth 


204  COMPENSATING    HETEROTROPIA. 

basal  centers  and  the  weak  superior  obliques  would  be  given 
rest.  In  such  a  case,  should  the  axes  of  the  cylinders  be 
reversed,  those  of.  plus  cylinders  in  the  upper  nasal  arcs, 
and  those  of  minus  cylinders  in  the  upper  temporal  arcs, 
they  would  become  unbearable,  for  they  would  compel  a 
compensating  minus  cyclotropia.  This  could  be  effected, 
not  by  tonicity  of  the  superior  obliques,  but  by  excessive 
contractility.  This  added  burden  cannot  be  borne  by  the 
right  and  left  sixth  basal  centers  and  the  two  superior 
obliques. 

Whether  the  artificial  non-symmetric  astigmatism  be  of 
one  kind  or  the  other,  the  images  are  equally  blurred;  but 
in  the  kind  exciting  tonicity  plus  cyclotropia,  there  is  com- 
fort, while  in  the  kind  exciting  contractile  minus  cyclotropia 
there  is  great  discomfort.  In  the  former  there  is  no  excite- 
ment of  basal  centers,  nor  is  there  contraction  of  the  ob- 
liques; in  the  latter,  the  right  and  left  sixth  basal  centers 
must  be  active  and  the  two  superior  obliques  must  be  con- 
tracting. 

Cylinders  given  for  the  correction  of  either  symmetric  or 
non-symmetric  astigmatism,  may  be  made  to  produce  an 
artificial  astigmatism  and  thus  create  a  compensating  cy- 
clotropia. This  is  accomplished  by  shifting  the  cylinders 
so  that  their  axes  are  no  longer  in  planes  with  the  meridians 
of  greatest  curvature,  if  the  cylinders  are  plus;  or  least 
curvature,  if  the  cylinders  are  minus.     If  the  obliques  are 


COMPENSATING    HETEROTROPIA.  205 

orthophoria,  any  displacement  of  the  axes  of  the  cylinders, 
in  opposite  directions,  will  excite  either  the  right  and  left 
sixth  basal  centers  and  the  superior  obliques;  or  the  right 
and  left  seventh  basal  centers  and  the  inferior  obliques, 
the  direction  of  the  shifting  determining  whether  it  shall 
be  the  one  set  of  centers  and  muscles  or  the  other.  If  there 
is  a  plus  cyclophoria  a  certain  shifting  of  the  cylinders  will 
cause  a  compensating  plus  cyclotropia  which  would  be  ef- 
fected by  tonicity  of  the  inferior  obliques.  This  would  re- 
lieve the  right  and  left  sixth  basal  centers,  and  the  superior 
oblique  muscles,  of  the  work  of  counteracting  the  cyclo- 
phoria. The  comfort  that  follows  is  a  full  justification  of 
the  procedure.  Had  the  axes  been  shifted  in  the  opposite 
direction,  in  this  case,  the  change  would  have  been  hurtful, 
in  that  it  would  have  demanded  of  the  already  over-worked 
sixth  basal  centers,  and  the  weak  superior  obliques,  the  pro- 
duction of  a  compensating  minus  cyclotropia. 

If  there  is  orthophoria  of  the  obliques,  the  axis  of  a  cylin- 
der should  never  be  rotated  out  of  the  plane  of  the  princi- 
pal meridian  before  which  it  stands,  for  the  reason  that  a 
basal  center  and  an  oblique  muscle  would  be  excited  by  such 
shifting.  If  there  is  a  plus  or  minus  cyclophoria  (the  for- 
mer is  common,  the  latter  is  uncommon),  correcting  cylin- 
ders may  be  shifted,  but  only  in  the  direction  that  will 
relieve  the  basal  centers  and  the  oblique  muscles  which  have 
always  been  active  in  counteracting  the  cyclophoria.     It  is 


206  COMPENSATING    HETEROTROPIA. 

not  going  too  far  to  say  that  the  axes  of  correcting  cylin- 
ders should  be  shifted  when  there  is  cyclophoria,  unless  this 
condition  can  be  relieved  by  exercising  the  weak  obliques, 
or  by  curing  the  condition,  in  suitable  cases,  by  operating 
on  a  rectus  muscle. 

When  the  axes  of  cylinders  are  shifted  to  relieve  cyclo- 
phoria, they  must  be  allowed  to  remain  at  the  new  points 
always,  that  the  effects  may  be  permanent.  When  axes 
of  cylinders  are  shifted  to  relieve  the  patient  of  annoying 
metamorphopsia,  the  aim  should  be  to  return  the  axes  to 
their  proper  places,  by  degrees,  and  as  soon  as  possible. 
Not  only  is  the  purpose  of  the  shifting,  for  cyclophoria, 
different  from  the  purpose  of  the  shifting,  for  metamor- 
phopsia, but  the  rules,  by  which  the  changes  are  made, 
differ  also.  The  rule  to  follow  when  there  is  metamorphop- 
sia can  be  found  on  page  196.  Dr.  N.  C.  Steele,  of  Chat- 
tanooga, a  life-long  friend  of  the  author,  and  himself  an 
earnest  student  of  the  ocular  muscles,  has  remodeled  his 
rules  for  shifting  cylinders  for  the  relief  of  cyclophoria,  as 
published  in  Ophthalmic  Myology.  The  author  requested 
Dr.  Steele  to  allow  him  to  publish,  in  this  chapter,  his  "work- 
ing rules,"  which  are  clear  and  simple.  These  are  the  Steele 
rules : 

"(1)  In  oblique  hyper  opic  astigmatism,  simple  or  com- 
pound, in  which  there  is  plus  cyclophoria  (weak  superior 
oblique  muscles)  and  the  upper  end  of  the  best  meridian  of 


COMPENSATING    HETEROTROPIA.  20? 

either  or  both  eyes  is  anywhere  in  the  upper  nasal  quadrant, 
and  you  are  in  doubt  as  to  the  exact  point  (degree)  at  which 
to  place  the  axis  of  the  plus  correcting  cylinder,  you  should 
place  it  as  far  from  the  center  of  that  quadrant  as  the  tests 
ivill  permit. 

"If  all  your  tests  have  indicated  one  point  (degree)  as 
the  correct  one  for  the  axis  of  the  cylinder,  it  is  advisable 
to  shift  the  axis  two  to  five  degrees  further  from  the  cen- 
ter of  the  quadrant — upper  nasal,  or,  what  is  the  same  thing 
in  effect,  the  lower  temporal  quadrant. 

"(2)  In  oblique  hyperopic  astigmatism,  simple  or  com.' 
pound,  in  which  there  is  plus  cyclophoria  (weak  superior 
oblique  muscles)  and  the  upper  end  of  the  best  meridian 
of  either  or  both  eyes  is  anywhere  in  the  upper  temporal 
quadrant,  and  you  are  in  doubt  as  to  the  exact  point  (degree) 
at  which  to  place  the  axis  of  the  plus  correcting  cylinder, 
you  should  place  it  as  near  the  center  of  that  quadrant 
as  the  tests  will  permit.  If  all  your  tests  have  indicated 
one  point  (degree)  as  the  correct  one  for  the  axis  of  the 
cylinder,  it  is  advisable  to  shift  the  axis  two  to  five  degrees 
nearer  the  center  of  the  quadrant — the  upper  temporal, 
or,  what  is  the  same  thing  in  effect,  the  loiver  nasal  one. 

"(3)  In  cases  having  minus  cyclophoria  (weak  inferior 
oblique  muscles)  the  foregoing  two  rules  should  be  re- 
versed. 

"  (4)  In  oblique  myopic  astigmatism,  simple  or  compound, 
all  the  three  foregoing  rules  should  be  reversed. 


208  COMPENSATING    HETEROTROPIA. 

"(5)  hi  mixed  oblique  astigmatism  the  first  two  rules 
hold  good  when  plus  correcting  cylinders  are  prescribed,  but 
when  minus  correcting  cylinders  are  prescribed  they  should 
be  reversed. 

"All  of  the  above  rules  apply  to  cases  in  which  there  is 
oblique  astigmatism  in  both  eyes,  and  in  cases  with  oblique 
astigmatism  in  one  eye  and  vertical  or  horizontal  astigma- 
tism in  the 'other,  and  in  cases  with  oblique  astigmatism  in 
one  eye  and  no  astigmatism  in  the  other." 

Vertical  and  horizontal  astigmatic  errors  are  often  asso- 
ciated with  plus  cyclophoria,  sometimes  with  minus  cyclo- 
phoria.  The  correcting  cylinders,  in  these  cases,  should  be 
shifted  for  the  developing  of  a  cyclotropia  that  will  cure 
the  cyclophoria.  If  there  is  plus  cyclophoria,  and  all  the 
monocular  tests  have  shown  that  the  best  meridian  of  each 
eye  is  at  either  90°  or  180°,  the  correcting  plus  cylinders 
should  have  their  axes  shifted  two  to  five  degrees  into  the 
upper  temporal  arcs,  or  the  correcting  minus  cylinders 
should  have  their  axes  shifted  two  to  five  degrees  into  the 
upper  nasal  arcs. 

The  above  rule  is  all  that  the  author  would  add  to  the 
Steele  rules ;  nor  does  he  see  that  anything  should  be  elim- 
inated from  these  rules. 

If  there  is  no  cyclophoria  complicating  a  case  of  astigma- 
tism, any  displacement  of  the  axes  of  the  correcting  cylin- 
ders, or  any  error  made  in  adjusting  them,  would  excite 


COMPENSATING    HETEROTROPIA.  209 

basal  brain  centers  and  the  oblique  muscles  under  their 
fusional  control.  Discomfort  would  as  certainly  result  as 
that  night  follows  the  day.  Nothing  could  emphasize  more 
strongly  the  fact  that  all  astigmatic  eyes  should  be  examined 
under  the  most  favorable  conditions,  and  that  all  available 
practical  means  should  be  used  in  locating  the  principal 
meridians,  and  in  determining  the  kind  and  quantity  of  the 
error.  These  are  the  favorable  conditions :  The  eyes  should 
be  under  the  influence  of  a  mydriatic,  and  each  eye  should 
be  tested  while  the  other  eye  is  covered.  The  mydriatic 
gives  the  static  relationship  of  the  anterior  focus  to  the 
retina.  The  monocular  test  guarantees  that  the  vertical 
axis  of  the  eye  under  test  is  parallel  with  the  median  plane 
of  the  head.  The  best  means  for  locating  the  anterior  pole 
and  the  axis  of  the  cylinder,  is  the  ophthalmometer;  and 
the  best  means  for  determining  the  strength  of  the  cylin- 
der and  whether  it  shall  be  plus  or  minus,  are  retinoscopy 
and  the  trial  lenses.  Although  indispensable  in  detecting 
intraocular  diseases,  the  ophthalmoscope  can  help  but  little 
in  the  work  of  refraction,  statements  to  the  contrary  not- 
withstanding. Last,  but  not  least  in  importance,  is  the  per- 
fect adjustment  of  the  spectacle  frames.  Patients  should 
always  be  told  that  a  straight-edge  should  pass  through 
the  four  joints  of  the  frames,  and  that  the  temple  pieces 
should  be  adjusted  so  as  to  prevent  an  inclining  of  the 
frames.     It  is  a  matter  for  regret  that  nose-glasses  were 

14 


210  COMPENSATING    HETEROTROPIA. 

ever  invented,  for  the  reason  that  it  is  so  hard  to  keep  them 
properly  adjusted. 

One  thing  deserving  emphasis,  in  closing  this  chapter,  is 
the  fact  that  the  man  or  woman  who  assumes  to  correct 
errors  of  refraction  and  muscle  errors  should  acquaint  him- 
self or  herself,  first  of  all,  with  human  anatomy  and  physiol- 
ogy, and  especially  with  that  most  wonderful  and  compli- 
cated part  of  man,  the  nervous  system,  which  presides  over 
the  nutrition,  and  controls  the  function,  of  every  other 
organ  and  part.  Nor  should  he  stop  with  a  perfected  knowl- 
edge of  anatomy  and  physiology,  but  he  should  acquire  a 
knowledge  of  general  and  special  pathology,  of  symptom- 
atology, of  chemistry,  of  materia  medica  and  general  and 
special  therapeutics.  In  other  words,  he  or  she  should  be 
required  to  complete  a  graded  course  of  study,  covering 
four  years,  in  a  reputable  medical  college;  for  correcting 
errors  of  refraction,  and  muscle  errors,  is  as  much  a  part  of 
the  practice  of  medicine,  as  is  the  treating  of  a  case  of  pneu- 
monia or  the  setting  of  a  broken  bone. 


INDEX. 


Ametropia  and  Pseudo-Heterophoria 134 

the  correction  of  160 

Area,  Retinal, 

of  binocular  fusion 39 

Axis  of  any  Rotation, 

how  to  find 6 

Astigmatism, 

symmetric 181 

nonsymmetric  181 

metamorphopsia,  through  correcting  cylinders  189 

hyperopic,  how  to  correct 193 

myopic,  how  to  correct 193 

Astigmatic  Accommodation 191,  192 

Anisometropia, 

a  cause  of  compensating  heterotopia 163 

Accommodation  and  Convergence 77 

Axes  of  all  Rotations 8 

Adduction, 

the  normal 41 

how  to  test 44 

Abductiom, 

the  normal 41 

how  to  test 43 

Adversion 29 

Abversion 29 

Binocular  Single  Vision  and  Basal  Centers 62 

Binocular  Rotations, 

in  the  four  cardinal  directions  10,     28 

in  oblique  directions 10,      1 1 


2i2  INDJEX. 

Binocular  Fusion  Field 39 

Bowman's  Muscle, 

nerve  supply  of 69 

its  work  in  neutralizing  corneal  astigmatism 192 

Brain, 

dominant  side  of 60 

centers,  cortical '. 58 

centers,  basal  ..57,  62 

and  muscle  rest  76 

Centers, 

conjugate  cortical 55,  58 

basal  57,  62 

first  conjugate 66 

second  conjugate : 66 

third  conjugate 67 

fourth  conjugate 69 

fifth  conjugate 67 

sixth  conjugate 72 

seventh  conjugate  67 

eighth  conjugate 69 

ninth  conjugate 67 

tenth  conjugate 67 

eleventh  conjugate 68 

Cardinal  Rotations  28 

Ciliary  Muscles, 

normal  and  subnormal  80 

super-normal 81 

Conjugate  Innervations 55,  68 

Convergence, 

how  to  test 35,  36 

normal,  how  effected 77 

angle  of 33 

size  of  angle  of,  how  to  find  33 

center  of 33 

conditions  that  modify 34 

and  accommodation 34 


INDEX.  213 

Cornea, 

decentration  of,  how  it  effects  vision 3 

how  to  detect 3 

Cyclo-Phorometer, 

how  to  use S3 

Cyclo-Duction 52 

Clclophoria, 

history  of  23 

varieties  of 116 

causes  of _ "6 

tests  for 21 

by  Moddox  prism 22 

by  single  prism 21 

by  rotary  prism 25 

by  the  Stevens'  clinoscope  27 

by  the  cyclo-phorometer  26 

treatment  of 120,  121 

by  rest  cylinders 203 

how  to  place  axis  of  cylinders  given  for  correction  of  estigmatism 206 

Corneal  Meridians 3 

Corneal  Refraction  Curves 5 

Contractility 28 

Cyclophoric  Eyes,  plus 1 16 

distant  seeing  of "6 

superversion  of  117 

subversion  of 120 

Cyclophoric  Eyes,  minus 121 

distant  seeing 121 

superversion  of 121 

subversion  of 124 

Cyclotropia, 

compensating i74>  2°3 

history  of  the  study  of 

caused  by  oblique  astigmatism 174-  x98 

how  retinal  images  are  displaced 174-  '91 

how  the  displaced  images  are  fused  174,  191 


2i4  INDEX. 

Cyclotropia, 

treatment  of,  by  correcting  cylinders  193 

annoyances  following  treatment  of 195 

Lippincott's  method  of  applying  correcting  cylinders 

to  lessen  metamorphoria   195 

Displacing  the  axes  of  the  fully  correcting  cylinders, 

to  lessen  metamorphopsia 196 

Cyclotropia, 

compensating 169 

plus 175,   180,  202 

minus 173,   176,  203 

Cylinders, 

adjustment  of 2.09 

displacement  of,  for  cyclophoria  205 

rule  for  shifting 206 

Decentration  of  Lenses 199 

Diplopia, 

nature's  two  methods  of  preventing 157 

Distortion  by  Cylinders 195 

Duction  Centers 38 

Duction  Power 38 

standard  of 41 

value  of 40 

low 51 

how  to  take 46 

how  determined  by  prisms  43 

how  determined  by  the  monocular  phorometer 47 

Emmetropic-orthophoric  Eyes _ 76 

distant  vision  of  76 

accommodation  of 77 

right  version  of 82 

left  version  of  83 

superversion  of 86 

subversion  of 86 

oblique  version  of 87-     93 

Emmetropic  Esophoric  Eyes 93 

distant  seeing  of 93 


INDEX.  215 

Emmetropic  Esophoric  Eyes, 

accommodation  of 96 

right  version  of 96 

left  version  of  97 

Emmetropic-exophoric  Eyes  105 

distant  seeing  of 105 

accommodation  of  105 

right  version  of no 

left  version  of in 

Emmetropic-hyperphoric  Eyes in 

distant  vision  of in 

su  perversion  of 113 

subversion  of 116 

Exophoria, 

test  for 19 

pseudo 37 

causes  of 37 

treatment  of,  by  concave  lenses 137,    140,   141,  143 

Esophoria, 

test  for .' 19 

pseudo  36 

causes  of 36 

how  it  manifests  itself 134 

treatment  of i49>   151,  161 

Esophoria, 

with  emmotropia 93 

with  hyperopia 150 

with  myopia 137 

symptoms  of,  caused  by 102 

Esotropia 152 

esophoria  as  a  cause 153 

hyperopia  as  a  cause 152 

amblyopia  of 157 

treatment  of 

by  convex  lenses 158 

by  the  amblyoscope 158 

operative  treatment  of  '5^ 


2i6  INDEX. 

Equator 5 

Equatorial  Plane 6,       7 

Fixed  Planes  of  the  Head 8 

Helmholtz '. 6 

Heterophoria, 

causes  of  true  128 

symptoms  of,  how  caused  130 

treatment  of '. 128 

Heterotropia, 

compensating 163 

caused  by  anisometropia 163 

caused  by  prisms  and  decentered  lenses 198,   199 

caused  by  displaced  anterior  pole 167 

caused  by  oblique  astigmatism 169 

Hyperphoria  and  Cataphoria m 

brain  centers  that  counteract m 

test  for 18 

Hyperopic-orthophoric  Eyes 145 

distant  vision  of 145 

convergence  of 149 

treatment  of 149 

Hyperopic-esophoric  Eyes 15° 

distant  and  near  vision  of 151 

treatment  of 154 

Hvperopic-exophoric  Eyes 158 

distant  and  near  vision  of 158 

treatment  of 160 

Innervations, 

cortical  or  conjugate 55 

basal  of  fusional 57 

Ideal  Eye 3 

Law, 

governing  the  recti 8 

governing  the  obliques  9 

Listing's  Plane 68 


INDEX.  217 

Lines  of  Direction, 

where  they  cross „ 184 

Lippincott 195 

Meridians, 

corneal  3 

Meridoinal  Planes 

are  rotation  planes 12 

Meridians, 

corresponding 171 

Metre-angle  of  Nagel 33 

variable  with  pupillary  distances 33 

Metamorphopsia  Through  Correcting  Cylinders 195 

why  it  disappears  more  quickly  in  some  cases  than  in  others 197 

how  to  modify 195 

rule  for  modifying  196 

Mortor  Nerves, 

the  third  pair 64,  65 

the  fourth  pair 70,  7 1 

the  sixth  pair 74,  75 

Muscle  Properties 

tonicity 13 

contractility 13 

Miller's  Muscle, 

nerve  supply  of 77 

function  of 77 

in  emmetropia 77.   80,  81 

in  hyperopia  145 

in  hyperopic  astigmatism  191 

in  myopia 136 

Muscles, 

pairs  of 13 

Myopic-orthophoric  Eyes -  135 

distant  vision  of 1 3  5 

convergence  of 136 


2i8  INDEX. 

Myopic-esophoric  Eyes 137 

distant  vision  of  137 

convergence  of _ _ 140 

Myopic-exophoric  Eyes 141 

distant  vision  of 141 

convergence  of 142 

treatment  of 141 

Nerve, 

the  right  third 63 

the  left  third  69 

the  right  fourth 72 

the  left  fourth  73 

the  right  sixth 73 

the  left  sixth 73 

Optic  Axis, 

so-called 1 

the  true 2 

Ocular  Muscles  and  Innervation  Centers, 

work  of 8 

Orthophoric  and  Heterophoric  Eyes  Contrasted 126 

Planes  of  Reference, 

medium  fixed  plane 8 

horizontal  fixed  plane  8 

Plane  of  Rotation  5 

Pseudo-esophoria  of  Emmeiropes 80 

treatment  of 82 

Pseudo-exophoria  of  Emmetropes 81 

treatment  of 82 

Poles, 

posterior  and  anterior  1 

how  to  locate  3 

Prisms, 

a  cause  of  compensating  heterotropia  198 

Primary  Position  of  Eye _ 76 


INDEX.  219 

Price's  Cyci.o-Phorometer, 

the  first  made 27 

Price,  George  H *7 

Phorombter, 

monocular  18 

Pose  and  Posture  in  Reading 32 

Retinal  Fusion  Area 18,  38 

Retinal  Meridians 2 

Rotation 5 

law  of 8 

axis  of 6 

plane  of — 5-  I2 

by  a  single  muscle 9 

in  the  four  cardinal  directions 10 

in  any  oblique  direction  10 

Steven's  Clinoscope 27 

tropometer  29 

Steel's  Rules  for  Placing 

axes  of  cylinders  in  cyclophoria 206 

Spectacle  Frames, 

how  to  adjust  200 

Sub-Duction 45 

Superduction    46 

Superversion 29 

Sub-Version 29 

Tests  for  Heterophoria 18 

Tendons, 

faulty  attachment  of 9 

Torsion, 

direction  of ll 

how  prevented lI 


220  INDEX. 

Tonicity  14 

equal,  gives  orthophoria 15 

unequal,  gives  heterophoria 15 

study  of  in  binocular  vision 17 

Tonicity  Tests, 

how  to  make 17 

of  the  obliques  21 

of  the  lateral  recti 19 

of  superior  and  inferior  recti 18 

Vertical  Axis  of  Eye, 

and  the  two  obliques _ 9 

Version  Power  28 

standard  of 29 

Verting  Centers  are  Conjugate 31 

Version, 

of  orthophoric  eyes 30 

of  heterophoric  eyes 30 

of  heterotropic  eyes  30 

Verting  Centers 31 

Version  Test, 

by  tropometer 29 

by  perimeter 29 

Visual  Axis, 

and  the  four  recti 8 

Version,  Right, 

of  orthophoric  eyes 82 

of  esophoric  eyes 96 

of  exophoric  eyes  110 

Version,  Left, 

of  orthophoric  eyes 83 

of  esophoric  eyes 97 

of  exophoric  eyes in 

Version,  Right  and  Left, 

in  accommodation  83 


IiNDEX.  221 

Version,  Super, 

of  orthophoric  eyes 86 

Version,  Sub, 

of  orthophoric  eyes 86 

Version, 

right-up _ 87 

left-down 92 

left-up  92 

right-down 93 


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